Fixed by part number. But if you describe what it is you're trying to do, there is often a workaround to accomplish your goal.

I have Novation Circuit Tracks. It can send 2 separate MIDI tracks through Ch 3 and 4. What would be the easiest way to integrate it with MODX so I can have these channels as separate MODX sound patches? What if I want for example to use multi-part A for Ch3 and multi-part B for Ch4?

You just can't do that. MIDI receive channels (for every Part) are not configurable to arbitrary values.

You can place all of the keyboard control=ON Parts on one channel (you can program that single channel) then address all of the keyboard control=off Parts by their respective Part # MIDI channels (Hybrid mode). This doesn't allow for 2 mutli-Part instruments on 2 different channels. It's one multi-Part (or more than a multi-Part) on a single MIDI channel and then all other Parts addressed one Part at a time.

In order to get where you're trying to get -- assuming you don't replace multi-Part instruments with single-Part ones -- is to take MIDI channel 3 and map it to multiple individual channels. This would be something between the Novation and MODX. There are hardware solutions and also software solutions that can re-channelize.

Novation ---> Ch 3 --> Rechanneled to replicate on Ch 1+2+3
Novation --> Ch 4 --> Rechanneled to replicate on Ch 4+5+6+7+8

Just an arbitrary example. So the Novation outputs Ch 3 but then something between (hardware only or computer+software) will re-channel this to 3 channels - to target say a 3-Part instrument. Then Ch 4 coming from Novation targets a 5-Part instrument and sends out on Ch4-8.

There isn't the configuration ability on the MODX side - so you'll need to get the outside MIDI messages to conform with what you have available.

Probably the very simplest way to get there would be to use single or hybrid MIDI mode. Set the MIDI channel to a configured single channel. Then externally address everything to that single channel and use either note or velocity range to differentiate between two different multi-Part instruments.

So say velocity 1-64 targets one instrument and velocity 65-127 targets the other. You'd get half the velocity "resolution" per part - but could adjust offsets to make this work even with the hit on velocity resolution.

Or you could use MIDI note range to map your instruments to lower/upper extremes of the MIDI note range and use some form of pitch correction (note shift) to either "octave(s) up" or "octave(s) down" the Part to place it back to a natural sounding range.

Assigning multiple Parts to receive on one single MIDI channel while also assigning multiple Parts to receive on a different single MIDI channel is off the table and incompatible with the instrument's capabilities.

I wish it were capable of this, but it isn't.

Thanks for the detailed answer. I guess using note range seems like a reasonable solution. I'll give it a try.

Thanks again.
Guy