There's a GM bank on MODX @ MSB=0/LSB=0/PC=0-127. Documented on page 187 of the data list (rev d).

MODX isn't GM or XG certified. There are some provisions to help - but if you don't like the built-in GM single-Part approximations for the GM set - you'll need to do some shuffling on your own. This would either involve creating a custom Performance on the MODX side (assuming the MIDI file does not switch sounds mid-stream. That each MIDI channel uses the same instrument throughout) - or editing the MIDI file itself to change the PC (program change) events to the proper MSB+LSB+PC that matches exactly the sound you're after. You could even sample something like a roland sound canvas (or perhaps buy the samples) and use software to generate a Library you can load into MODX so you have a new set of sounds that represent the GM sounds you want. Then the MSB/LSB/PC would point to that library's sound(s).

I have quit a large collection of GM files that I want to record as audio in Cubase.
The GM files was sounding ok with my previous keyboard - Yamaha Genos - but I feel the GM voices
in MODX is lacking a bit in quality comparing to the Genos. I therefore thinking of replacing the GM voices with better performance patches and I'm trying to understand the recommended workflow to achieve this.

Many people wrongly equate GM compatible with quality of sound. Wrongly, because as you have discovered, it has very little to do with the price. GM compatibility refers to a set of rules that setup a minimum requirement for the sounds that qualify — the rules guarantee the response of the listed sound, that it can be delivered with the appropriate polyphony, with the appropriate EG, the appropriate number of layers in the sounds, the velocity switch points in sounds that respond to articulations (like ‘slap bass’) they only have access to two system effects, etc., etc.

Because the GM soundset’s rules do not require that edits to the various Voices be stored on the product, but are instead ‘stored’ as CC, Sysex, NRPNs, etc data in a Setup Measure located at the top of the file, the product can, if desired by the manufacturer, be made a lot less expensive.

These rules allow for GM sound sets to be made very inexpensively by the manufacturer of a GM product. It does not mean that you *have to* make it inexpensively, obviously products can easily exceed the basic requirements and give you highly detailed and nuanced sounds that can be stored in internal memory, and these can be used to substitute for any on the GM list... as with Genos, for example.

So how do you tell if a product conforms to the official General MIDI rules?Easy...
It will have the official GM logo emblazoned on the product somewhere. The GENOS, like most Yamaha PSR-E series, PSR-S series, Tyros Arranger/Digital Workstation products feature GM, GM2, GS and/or XG logos (all voicing protocols)... and they officially conform to the rules of those systems.

The synthesizers in Yamaha lineup do not feature the GM, GM2, nor XG, GS logos, and they do not conform to the official rules of these protocols. What you find in the Yamaha synthesizers is a pseudo-GM set, in the case of your MODX or MONTAGE, you’ll find a bank of 128 Normal programs that will serve to replace a GM listed program — even though it is clearly a MODX/MONTAGE level sound — they will dutifully respond to the GM Bank and Program selections.

The Yamaha synthesizers, unlike some competing manufacturers, are not using a separate tone generator chip slapped in the product to comply with official rules... instead the MODX’s pseudo-GM recalled Program 001 is actually “Concert Grand Piano” made from exactly the architecture that makes up any other program found in the synth... that means it has the same architecture, the same envelopes, access to the synthesizer’s 18 Filter Types, access to the same Effect Routing, the same 8 Element architecture as every other AWM2 Normal program... (allowing the synth user to improve on the selection/make it their own!)

Because the GM rules do not require such elaborate architecture, selection of filters, advanced envelope generators, insertion effects, etc... you have an opportunity to substitute any program in the place of the one selected by the original author of the General MIDI File. In that Setup Measure, the File’s author can set a Bank Select MSB/LSB (000/000) and Program Change (000-127) to select each Track’s instrument.
GM Drum kits (127/000) - there are 9 GM Kits on the official list.
The pseudo-GM set in the MODX has just one GM Stereo Kit (although most of the MODX Kits follow GM mapping).

A Bank Select/Program Change = 000/000/000 selects an Acoustic Piano on all GM and pseudo-GM products. On an official GM product, your first listed sound is always a Grand Piano (suitable for Classical/Jazz)... it will have a Send amount to the System Reverb and another to a Chorus/(delay) effect... on the MODX/MONTAGE you can actually choose any of the powerful boutique effects found in the synth’s huge library of Effects... including assigning two Insertion Effects exclusively for this instrument selection!

A Bank Select/Program Change = 000/000/034 selects a Fingered Electric Bass... on a basic GM sound set this typically means a Fender Precision type electric bass, on a basic XG sound set, at Program Change 034 (but with a different MSB/LSB) you could select a Music Man electric fingered bass, or an Alembic electric fingered bass, or even a Rickenbacher electric fingered bass (all have a different character substitute), etc., etc., etc. XG is Yamaha’s extended set of GM compatible sounds... same PC# but found in a parallel Bank.
* the GS sound set protocol is Roland Corp. extended set of GM substitutions and controller responses.
* the MODX’s native sounds have their own MSB/LSB and PC numbers.

Extend this concept to the unlimited number of substitutes you could select from the MODX/MONTAGE sound libraries... when you have a MODX, the GM File may request 000-000-034 (the standard) fingered electric bass... and playing back your GM File that is what will be selected... you can choose any bass sound you desire.

In fact this is what the pseudo-GM Bank is all about... CHOICE. if it works, fine use it. The MODX will call up a decent substitute (a flute will be a flute, a trumpet a trumpet, and an electric fingered bass will be an electric fingered bass, and so on), you can improve it by selecting whichever Electric Bass (or any sound) you desire. You can either edit the message in the track MSB-LSB-PC (the hard long way) or you can simply use the MODX’s internal engine to STORE your selections in a User Performance named for the song your constructing. (You can eliminate that GM Setup Measure because all of your sound edits are stored in the synthesizers onboard RAM).

GM products do not require the (expensive) type of memory that can store the hundreds and hundreds of parameter settings that make up a 16-Part program... remember, all that stuff is Sent on Track-by-Track basis to the tone generate (making it possible to make a GM sound set incredible inexpensive to make!). In GM,GS,XG all Parts are Reset to GM defaults by the first message on Track 1 — which is always the GM RESET sysex message. When this is received by the device it resets all Parts to the Concert Grand, except 10 which recalls a GM Drum Kit, all volume to a specific setting, it zeros out the mix, all Parts panned to Center, etc., etc.
The MODX has this expensive type of memory, therefore, it can store the hundreds of parameter settings per Part and can store hundreds of Performances....

Let's say I have a GM file that are using 16 midi channel. The first midi track is using the GM Acoustic Grand Piano on midi channel 1 and I want to exchange this voice with a Piano performance that's using 4 parts. Should I create 4 new midi track in Cubase and assign them with midi channel 1-4 and temporary disable the other midi tracks that are using channel 1-4 and then record the the performance as audio and then repeat the whole process with the rest of the tracks? Or is there a simpler workflow to achieve this?

You would need to do a ton of work to start substituting Multi Part instruments for the (single) Part GM selections of the author. See below... GM *rules* require a separate Part and Channel for each instrument...

Some other related questions. When using the Genos, there was an application called MegaEnhancer, that replaced the GM voices with better sounding instruments, but I guess this application will not work with the MODX?

Enter the MegaEnhancer... this is exactly what this program does, in essence... it does the work for you in the world of the GENOS.

Yamaha, recognizing that musicians will always listen to the original author’s work, and decide that it would sound better with MY SELECTIONS, this is what we are talking about here - improving or at least changing the originally programmed selection. That Mega Enhancer represents (as you are discovering) a whole truckload of work... doing it manually (as you will need to do with the MODX/MONTAGE) will make you really appreciate just what a great thing that utility is... lol.

(With the synthesizers, Yamaha assumes the customer *wants* to do this substitution yourself... plus with all the custom sound locations in the synth, naturally, you get to choose).

Not all GM/GM2/XG products have such a thing as the MegaEnhancer...
With the synthesizers YOU are the “enhancer” — and it does, indeed, takes a bunch of work. (I’ve been here, done this, and have several T-shirts!!! As you may imagine).

The MODX/MONTAGE are 16 Part multi timbral... so once you start substituting Multi Part instruments for the GM protocol’s strictly Single Part Voices, you will run out of Parts quicker— for sure. If your goal is to keep the finished product as a MIDI File you must select your sounds wisely so as to not exceed the limit (16 Parts) — otherwise you’ll need to purchase a second MODX. lol

AUDIO, as you surmised correctly, can be the target for each MULTI PART instrument you wish to use.

If you are using Cubase, say you wish to use the Multi Part (4) “CFX Concert” in place of the standard Single pseudo-GM substitute, “Concert Grand Piano”:

One workflow would be to do an instrument at a time...
Call up the “CFX Concert” Performance
You can use the “MIDI I/O Mode” to set all four Parts to respond to a single MIDI channel (Single, Hybrid)
Press [UTILITY] > “Settings” > “Advanced”
MIDI I/O Mode = Single means the selected KBD CTRL Performance will Receive/Transmit on a Single Channel
MIDI I/O Mode = Hybrid is the same as Single, except all non-KBD CTL linked Parts continue to Transmit and Receive on their correspondingly numbered MIDI Channel.
Set the I/O Channel to the Channel playing back the piano data.
Solo that Track in Cubase.

I recommend recording the Audio without Reverb... this way you can determine *how much* when you have assembled all Parts as separate Audio Tracks. (But that is, again, your choice).

I was looking in the MODX data list manual and tried to find which MSB and Program Change Message each voices where using, but couldn't find any information about this. Is it because MODX is using multi part voices instead o single parts? On the Genos it was quite easy to find a replacement voice for the GM just by looking at the voice mapping.

Each Single Part MODX program will display the MSB/LSB/ and Program Number right in the screen.

Like other Yamaha products, the Single Part MODX programs (the ones listed in green in the Performance [CATEGORY SEARCH] screen) will show you the Bank and Program. Say you want to use the Single AWM2 Acoustic Piano “S700 for Montage”...
From the HOME screen:
Press [CATEGORY]
Set “Bank/Favorite” = Preset
Set “Attribute” = Single
Tap “Piano”
Select “S700 for Montage”
On its HOME screen, tap the box for Part slot 1, the “Type/Name” box
A pop-in menu appears from the left
Tap “Property”
The screen will report the MSB 63 (all Single Part programs will have MSB 63)
The LSB (the MODX Bank of 128 it comes from)
And the Program Change No. listed 1-128*** (the actual Program Change is one less since most DAWs use 0-127)

MSB = 63
LSB = 0
PC# = 019 (or 018 when inputting to DAW)

Extra Credit:
Taking apart the file and transferring an instrument at a time, is no more work than it took to create the tracks in the first place... in fact, it is exactly the same except the actual performing (the hard part) is already done by the file’s author.

Because when substituting sounds the behavior can be different, there are several things that simply will translate in a bizarre fashion.
Examples:
__ If the GM file uses the CC74 (Cutoff) and CC71 (Resonance) extensively, some authors use it lieu of not having an EQ (not required in a basic GM engine) GM engines are not required to have individual Part EQs, your MODX gives both a 3-band EQ Pre- Insertion Effects, and a 2-band EQ Post- Insertion Effects, per Part.... the “killer” Filters in the MODX engine may send that sound howling off into the distance

...as you might imagine the Filters in a product like the MODX are a bit more responsive than your run of the mill GM system. You may find the filters go into self-oscillation (usually not available on inexpensive GM modules).

__ If the GM file uses a Bass sound, you will discover that most of the Yamaha bass sounds that are not apart of the pseudo-GM set are an octave off from the GM standard. Yamaha basses are typically an octave higher than the standard GM basses... recognizing that if you have a 61 note keyboard you might want to reach the low E on a bass without having to Transpose the Octave. GM bass require a 76 or 88 note keybed to play the bass in its proper range - meaning you must shift octave in order to play the bass from a 61 note controller.

Thanks guys. I really appreciate the detailed answers and I've learned a lot. It will for sure help me going forward and understand the MODX architecture and workflow.
I was playing around with the MODX connect yesterday and this is an amazing tool when working with Cubase and will make the workflow a lot easier.

Cheers
/Jugge