What is Synthesia?

If you are connecting the MODX to a computer there is one driver. You say you have “all the drivers” - we assume you have the correct one for your computer type (which you also don’t mention).

Connect the USB “To Host” port to your computer
Make sure the MODX is set to MIDI I/O = USB ... Press [UTILITY] > “Settings” > “MIDI I/O” > “USB” should be green (active)
When you have a good connection to your computer, the USB icon on the top line of your MODX screen will glow bright blue.

Let us know.

Synthesia is a software that reads midi files. And when a synthesizer is connected, you can learn how to play songs, it's like a game where the note are falling on a keyboard and you have to press the right key to keep the song going ! I invite you to do a quick search if you don't see what I mean!
Since the software recognize the MODX both in output and input but no sound is coming out, I supposed it was a MODX setting problem!

By all the drivers, I meant, Yamaha Steinberg USB Driver V1.10.4 and MODX Connect for windows! Sorry it's the first time I post something on a forum, I didn't know what to say exactly.

Like I said, everything is, in theory, well connected, "USB" on "Settings” > “MIDI I/O" is green, and the USB icon on the top is blue, that's why I don't really understand what's wrong!

I don't have much knowledge about Midi stuff, but my theories is that there is a problem with MIDI channels! If i am correct, each instrument on a midi file is on a differents MIDI channels, and it seems that my MODX can only read one channel with the wrong instrument! So I thought that I could solved that by setting the MODX on "MULTI" in [UTILITY] > “Settings” > "Advanced" > "MIDI I/O MODE" but I have the same result...

Sorry if I'm a bit clumsy, English is not my native language.
Also thank you for trying to help!

On the MODX (we can only really help you with the MODX)
Press [CATEGORY]
Set “Bank/Favorite” = All
Set “Attribute” = All
Touch “Init”
Select “Multi/GM”

This will place an instrument in each Part 1-16 and is the basic starting point for using the MODX as a 16 Part multi-timbral tone generator... like when working with MIDI Files.

Well It kinda solve the thing! all the midi channel are playing, but they all produce the piano sound! I suppose it's a normal thing since all the 16 part are piano acoustic type? Is there a way to change that? I can edit all the part but I can't really change the instrument.

Once again thank you for your help and your time, I really appreciate.

edit: I found the solution! I just had to look at the MIDI channel of all the instrument in the MIDI files, and add the instrument on the parts that correspond on the MODX! Like if there is a nylon guitar on MIDI Channel 5, I create the part 5 with a nylon guitar and everything works fine!
I only have one question to ask! I noticed that on some files, there is more than one instrument on one MIDI channel, do you know if it's possible to change the MIDI channel of an instrument? I don't think it's possible on the MODX since you can only have one instrument per parts if I'm correct?

If there's more than one instrument on a track then that track would need to issue a program change message to "call up" the new sound. The Init/GM should respond well to PC changes as I believe the MSB/LSB already assumes the GM sound bank - so PC changes would call up the closest MODX equivalent to the GM sound for that given PC.

If your original MIDI file had PC changes embedded - then you shouldn't need to pre-program the PARTs with different instruments (nylon guitar, etc). Although that is a way to build a Performance to more correctly play MIDI files.

So I shouldn't have that piano sound everywhere...

Also in Cubase > "Studio Setup" > "VST Audio System" > "ASIO Driver"; I don't have "MODX" but "Yamaha Steinber USB ASIO"! Is There a connection with my problem or "MODX" and "Yamaha Steinber USB ASIO" are the same thing?

The “Multi/GM” is similar to the default starting point designed for using General MIDI files or as a starting point for creating 16-Part multi-timbral setups for use with a sequencer. It places a “placeholder” program in each of the 16 Parts. The “Concert Grand Piano” in all slots, except Part 10 which is set to “Stereo GM Kit”. MIDI Files can contain Program Changes to select the specific instrument on a Track-by-Track basis. Or you can manually select a different instrument for each Part as you may desire.

If you are not familiar with General MIDI, you can Google it... (a standard protocol for song sharing via MIDI).

The GM sound set includes 128 “normal” instruments, arranged in 16 categories, 8 instruments per category. For example, It starts with the Piano/Keyboard category...
An acoustic piano (classical/jazz) 001, a bright acoustic piano (rock/pop) 002, a CP80 (electro-magnetic) 003, a honky-tonk piano (detuned) 004, a Rhodes (tine electric) 005, a DX type (digital electric) 006, a Harpsichord 007, and a Clavinet 008.

This category is followed by 8 “Chromatic Percussion” instruments, then 8 Organs, 8 Guitars, 8 Basses, 8 Strings, 8 Brass, etc., etc. The concept allows different products to recall a similar instrument to the one selected by the MIDI File’s author. GM program #033 will always recall an acoustic bass sound on all compatible products. You select the instrument you wish for each of the 16 Parts. The “Concert GrandPiano” simply happens to be sound #001 of the list of 128 normal instruments. Channel 10 is reserved in GM for “drums” this is why Part 10 has a drum Kit by default.

The “Multi/GM” is just a template, a starting point for setting up to use the synth as a multi-timbral tone engine.
You have an “Init” for building Performances from an AWM2 engine
An “Init” for building a Performance from an FM-X engine
You have an initialized Drum Kit,

Your MODX has some 2,195 factory program Performances... of these 128 normal instruments and a GM-compatible drum Kit have been set to respond to the Bank Select and Program Change protocol of the GM system. We are not familiar with the program (Synthesia) that you mention but assume it uses this protocol if it involves generic MIDI files

Windows computers identify the selected Audio Streaming Input Output (ASIO) Driver by its name: in this case “Yamaha Steinberg USB ASIO”.
In Macintosh computers the selected driver is identified by the specific product model, “MODX”, that is using it.
What you see listed will depend on the computer type you are using.

In Synthesia's settings, under "Advanced" make sure that "Instrument Change Messages" is turned on. You can also try turning on "Bank Select Messages".

Also make sure that on the MODX, Pgm Change is set to On under [UTILITY] -> [Settings] -> [Advanced].