For example I would have a performance with 4 parts. Two parts are played from the MODX and the other parts would be on a different MIDI channel (i.e 11) and played from the Nord Stage 3.

For a Performance which contains two MODX parts you'd like to play from the Nord Stage 3, make those sounds, for example, Part 11 and Part 12. Then on your NS3, set up the program with two EXT functions enabled, set one for channel 11 and the other for channel 12. (They don't have to be 11 and 12, you can use any two between 9 and 16 inclusive, just remember that the MODX part number equals the Nord MIDI channel you'll have to choose.) For the other two sounds which you want to play directly from the MODX' own keys, put them on parts 1 and 2 (or any two of the first eight parts). You can actually have up to 8 parts actve for the MODX to play itself. However, since the Nord only supports two EXT channels within a single Program, the Nord will be limited to playing no more than two MODX parts at a time.

The distinction from your current workflow is that while the Korg allows for you to change the MIDI receive channel for different patches, MODX does not allow for setting the MIDI receive channels. Therefore, the responsibility is on the transmit side (Nord Stage) to match the fixed incoming MIDI channel assigned to a MODX Part. This is what influenced the instructions Scott has presented.

Not advising you change anything, but FYI:

If you chose to swap designation of the master controller, MODX has assignable MIDI channels on the transmit side. PARTs 1-8 are under direct keyboard control and all of these PARTs can be assigned an arbitrary MIDI channel for transmit. This is set up using "Zone Master" (global setting: switched on) and PART-level Zone configuration (allowing assignment of MIDI channel, volume, pan, MSB/LSB/PC transmit when the Performance is recalled). Each of these settings (volume, pan, MSB/LSB/PC, channel) is optional as you can opt out of sending any of these for a zone configuration.

Thank-you for the valuable information.

Jason, I have considered swapping the Master Controller roles.

However, my main keyboard is the NS3. The MODX is part of my extended rig.

Another config:

Would switching the MIDI I/O Mode from Multi to Single be give any advantages?

Since it's one MIDI channel for all parts, I could play all parts from the NS3 rather than just a maximum of two.

I would only enable the Nord Stage External Section when needed.

For the Performance parts that I want to be played on the MODX, I would enable the Keybd Control, other parts in the Performance I would not.

Would that work?

Thanks for your time and help.

Here's another possible approach that I think will work (I'm new enough to the MODX to not be certain)... Put the sounds you want to play from the MODX' own keys on parts 1 and 2; put the sounds you want to trigger remotely form the Nord on parts 3 and 4. Set the Nord's EXT channels to 3 and 4, and on the MODX, set parts 3 and 4 to not respond to the MODX's own keys (turn off Keyboard Control). Assuming this works, the advantage of using parts 1 through 4 (instead of two of the first eight and two of the second eight as I described above) s that you'd have seamless sound transition when switching to another Performance (assuming that Performance likewise had no more than four parts).

To Jason or anyone else, is this correct? And related, am I right that, in order for SSS to work, not only do you have to be using no more than four parts, but also none of the four can be located in 9 through 16?

Would switching the MIDI I/O Mode from Multi to Single be give any advantages?

As I understand it, this would allow you to play up to 8 MODX Parts from the Nord, layered with the Nord's own sounds. The downside is that the MODX' own keys can't play anything other than those same 8 parts. I don't think any Keyboard Control settings will make any difference... I think it considers the external keys to simply mirror the internal ones, so whatever turns the internal ones on and off will have the same effect on the external ones. I think. 😉

If you want to play select PARTs from an external controller, single-channel is not the route to take. If all MODX PARTs are meant to be triggered by an external controller, single-channel MIDI mode is an option.

I don't have a MODX to test if 4 parts means any 4 out of the 1st 8 or only PARTs 1-4. I see no real benefit in using non-contiguous PARTs so I personally would stick to only PARTs 1-4 if I wanted SSS to work (and assign none in PARTs 5-16).

You really have to examine if it's worth placing this extra constraint on your setup in order to gain the facility of SSS. There are so many other ways to achieve the result that SSS gives you without actually using SSS. For me, MODX's extra constraints further diminishes the utility of SSS vs. other priority goals - having the sounds "in front of me" for a tune that I would be hard-pressed to aim for SSS vs. using other techniques to switch sounds.

In a 2-keyboard setup where each keyboard can "ping pong" - meaning both do not change Performances/patches/programs/combis/etc. at the same time - you can "hold the fort" with one keyboard while changing the sounds on the other keyboard. This is intrinsically already a form of "SSS" using two different keyboards. The necessity for yet another layer of "SSS" in this situation may not be very high. This is a generalization, so your own needs may vary.

Ok so I will leave the MODX in Multi Mode and then assign NS3 External Section to transmit on MIDI channels 3 and/or 4 so it can play the MODX parts.

Thank-you both for your help!

I don't have a MODX to test if 4 parts means any 4 out of the 1st 8 or only PARTs 1-4. I see no real benefit in using non-contiguous PARTs so I personally would stick to only PARTs 1-4 if I wanted SSS to work (and assign none in PARTs 5-16).

It is only the first 4 parts. If you only have 4 parts but using parts 1,2,4,5 you won't have SSS. I just tested it.