I will read those articles, see if I can get a solution.

I have done nothing with zones on MODX, only on Impulse.

So impulse is sending 3 zones channel 6,7 and 8.
Everything is connected with USB. So the Impulse via USB to device of the MODX and mainstage by USB to host on the modx.

In a pratical situation I have for example:
Performance on modx with the first two parts on a Rhodes keys and part 6 and 7 I have a horn section.
6 and 7 have no keyboard control, so the impulse playes the horns and the modx the rhodes. Everything fine. In this scenario channel 8 played by impulse is also received by mainstage.
2nd example:
The CFX grand performance with parts 1-4 played by modx. No parts on 5-8. Mainstage will not respond to channel 8 in this case.
If I add a dummy sound on channel 5 (without Keyboard control) it works and now channel 8 is received by mainstage (played by impulse).

You didn't elaborate, but I'm going to assume the Impulse is connected to the "USB TO DEVICE" port (and not "USB TO HOST" port)...

Since you are connecting the Impulse to the USB TO DEVICE port, your impulse is going to be transmitting on any Part(s) that have keyboard control turned on. Naturally, empty slots have keyboard control turned off. Every Performance has Part 1 (it must exist) and your Impulse will always be transmitting on that Part if keyboard control is turned on (or if it is not and Part 1 is selected).

The MIDI configuration of the Impulse isn't really respected when using "USB TO DEVICE".

Another option would be to use the 5-pin DIN on the Novation Impulse. This provides a better way to direct MIDI traffic from the Novation through MODX. In fact, it's more in-line with this usage model altogether since the instrument itself will not receive the MIDI data. Instead, the data will only go THRU your MODX.

When this is done, Mainstage will communicate to the Novation using MODX Port 3 (sometimes shown as "MODX-3" ).

For further information, see the "USB" heading of: https://www.yamahasynth.com/learn/modx/mastering-modx-midi-settings-explained

When you want MODX to receive MIDI from your Impulse, you would have Mainstage route the MIDI back to MODX Port 1 ("MODX-1" ) and Mainstage should be able to direct the MIDI to any channel you wish. I'm not a Mainstage user - but I'm sure it can handle MIDI routing.

Also, if you use zones as has been hinted at - that does give your MODX more control over MIDI routing. However, that also forces you build a custom Performance for everything since Zones are not used in any factory presets. I take it this would be not desired from what you've already communicated. Which is fine.

@jason:

Indeed, My Impulse is connected through the USB to device port.
Your assertion that Impulse sends on all parts with KEyboard control turned on isn't correct.
In my performance with horns on 6 and 7 (and rhodes on 1 and 2) I have the keyboard control turned on on the rhodes and not on the horns. The result is that impulse plays the horns and modx plays the rhodes.
Likewise when I have a performance with part 1-4 filled with keyboard control on and a dummy sound on 5 (without keyboard control so the modx won't play it), channel 8 coming from the Impulse is routed to Mainstage.
So it seems MODX respects the zone/channel settings of the Impulse and the channel doesn't necessarily have to be filled to put through the MIDI (in my example with channel 5 filled as dummy channel 8 is empty, but still sends midi to Mainstage).

The option to use DIN for midi from impulse to MODX is not an option. Reason is that I also need the USB MIDI out to mainstage from MODX to Mainstage (for the purpose of MIDI clock from mainstage, program changes from mainstage to MODX and the use of MODX as Audio Interface. The MODX requires me to choose between DIN or USB, so that combination is not going to work.

Using Mainstage as MIDI Thru might be a good tip, gonna try if that works, although it would take up a USB bus on my mac, that might be a problem when I have to use a 3rd USB input (then it would require a seperate USB hub and i am trying to avoid that.

I think ultimately I have to accept that for songs that need Impulse to control mainstage, I have to make a custom performance one way or the other. If I am lucky I can be done with making a view standard patches with standard instruments (mostly the MODX will have piano's or Rhodes) with such a MIDI setup.

Thanx for your answer though!.

MIDI out from Mainstage to MODX would be via Port 1. That was part of the setup suggested and would also be used to echo messages from MODX Port 3 to Port 1. MODX Port 1 is the tone generator. MODX Port 3 is USB DIN Thru.

BTW: I've got a Novation on order so I can test this better. I've got a USB controller that cannot set any "zones" (always Ch1). I see sending to MIDI channels from the USB-connected "USB TO DEVICE" respects the Part #s for reception.

Still, sending to Channel 1 will always work because Channel 1 is always there.

The MODX requires me to choose between DIN or USB, so that combination is not going to work.

I'm not sure you understand that 5-pin DIN works under USB mode. Here's the rundown:

Under "MIDI" mode, the 5-pin DIN connected keyboard(s) are sending/receiving MIDI to/from the MODX tone generator. So these will be able to directly communicate with MODX's Parts. If this were a USB mode, then this would be MODX USB Port 1 (tone generator). Of course in this mode, the USB is inactive.

Under "USB" mode, the 5-pin DIN is connected to MIDI THRU to USB (MODX Driver) Port 3. So, yes, absolutely the 5-pin DIN is available to your DAW (Mainstage) using Port 3. Not everyone is aware of this and there are pages of requests on Ideascale asking for essentially a feature that's already supported. Certainly for those who already have a DAW as part of their standard configuration.

Using Mainstage as MIDI Thru might be a good tip, gonna try if that works, although it would take up a USB bus on my mac, that might be a problem when I have to use a 3rd USB input (then it would require a seperate USB hub and i am trying to avoid that.

I think this is another misunderstanding. Do you already have a USB connection from MODX's "USB TO HOST" port to your mac? For Audio/MIDI/both? If so, then MODX Port 3 is already on this same USB connection. The link provided summarized what's going over USB:

Single USB Cable =
MODX Port-1 which is the MODX Tone Generator, local controllers (knobs, buttons, etc). Audio channels and MIDI
MODX Port-2 which is the DAW remote
MODX Port-3 which is the MODX 5-pin DIN bus (MIDI only)

Ignoring DAW remote, your DAW would route Port-1 and/or Port-3 appropriately to target the local keyboard or an external 5-pin DIN connector. DAW remote is ignored for simplicity (this thread ... not needed as far as I can tell).

I got my Novation in today. Now I have a USB MIDI device I can easily change MIDI channels.

With the MODX in multi-channel MIDI mode using an external MIDI device connected to the USB TO DEVICE port:

If the transmit channel on the Novation matches a Part with Keyboard Control=ON, then all Parts with Keyboard Control=ON will play simultaneously.

If the transmit channel on the Novation matches a Part with Keyboard Control=OFF, then only that single Part will be triggered.

Which Part is selected (on the MODX) does not factor into what the external device triggers. Say Parts 5-6 have keyboard control off - if the USB-connected MIDI controller is set to Channel 5 then the external controller will trigger Part 5 even if locally MODX has Part 6 selected and the local keys can only play that single Part when Part 6 is selected. In other words, part selection is ignored for this external USB MIDI connection.

Indeed, the midi from Impulse to Modx is working fine. Correspond the midi send with the right parts and it all works (when you set the local controls right).
My problem is that when zone 3 of the impulse is set to for example channel 8 (and you have the impulse connected with MODX via USB to Device and MODX to Mainstage via USB to Host, it does nothing when parts 5-8 are empty.
I now use a 'workaround' with using an extra din cable and that seems to work when using port 3 on mainstage.
But it still feels like a flaw in design. I can't imagine what the reason is why MODX puts channel 8 thru when one of the parts of 5-8 is filled (doesn't necessarily have to be 8) but doesn't send thru channel 8 when there is nothing set in 5-8.

But hey... its only one extra cable to get it working, so no harm done. 🙂

Port 3 works because it bypasses the Parts completely. Port 3 is really just a virtual USB-to-MIDI cable:

Now, having any USB-MIDI device connected to the TO DEVICE port is a new development. Later in the release of Montage/MODX - this feature was added as a response to user requests. There may be internal architecture preventing passing through MIDI on an empty Part as this generation has new motion control, motion sequence, etc. features that may have an impact here - but you can always make a request to modify the behavior on ideascale ( https://yamahasynth.ideascale.com). That's for the long game as it takes a while for ideas to go through the process. This kind of idea seems inline with the sort of thing picked up.

I think the pushback would be to create a user performance with the Part(s) you want to pass MIDI instantiated. But it's worth a shot. And yes, Port 3 is easier to deal with since it works today.

But the strange thing in this situation is that it is not that it will not pass midi on an empty part. It will, but only if another part is filled of the 4 parts it belongs to (1-4, 5-8 etc). And particularly that is what's confusing me. If it was the case that only midi is passed through a channel that has the corresponding part filled, would also be weird to me, but that would have some logic to it.

Adding a part to a performance works, but as said: the extra midi cable is more easy. Because this way I don't have to make a user performance for everytime I use a factory performance with midi controlling mainstage alongside.

I already put this on Ideascale, curious if and when it will be picked up.