From what I gather, you want to play MODX7 piano keys and want a range of keys on the left side of MODX7 to transmit on MIDI channel 1 and the rest of the keys (on right side of the MODX7) to transmit on MIDI channel 2. The left side, although transmitting on channel 1, is not really targeting the VK8M since it will not be configured to respond to MIDI channel 1. Instead, the left side of the MODX7 is meant to be used for an internal sound: bass guitar. The right side is for external control only without any sound generated by the MODX7.

I just wasn't sure if you ever wanted to play any keys on the VK8M for the MODX7 to receive and respond to - but I'm assuming this is not the case.

Yes, you can do that. Zone control is a way - although you don't necessarily have to do it if all you need is note on/off messages on MIDI Channel 2 for external control and bass guitar on MIDI channel 1.

Here's the simple way (without Zone Control):

1) Place MODX7 in multi-channel MIDI mode (this is MODX's factory initialization default). [UTILITY] then “Settings” -> “Advanced” - MIDI I/O mode parameter
2) Recall a single-PART bass guitar Performance. Most bass guitars in MODX are single-PART - so this isn't much of a limitation on your choices. This will, by definition, place the bass guitar on PART 1. PART 1 in multi-channel MIDI mode will transmit on MIDI Channel 1. Note: search for the bass guitar should use [CATEGORY SEARCH] and you can filter by single-PART Performances and then choose the bass category and appropriate sub-category if desired
3) From [PERFORMANCE] (HOME), press the [+] button to add PART 2 and choose any single-PART organ part. It doesn't matter which one you choose. I say to pick organ only so the screen can show "organ" as a reference. We'll configure PART 2 not to trigger the internal tone generator so it is external only. By definition, PART 2 will transmit on MIDI Channel 2
4) MUTE PART 2 - this ensures PART 2 will not trigger any elements (internal oscillators). "Mute" does not prevent MIDI messages from being transmitted from PART 2 (MIDI channel 2).

That's quick-and-dirty. The "dirty" part about this is that your VK8M will "see" MIDI traffic on channel 1 and channel 2 (PART 1 and PART 2). The traffic will be a carbon copy on both. This isn't such a big deal if the VK8M "ignores" channel 1 - but it's still more traffic. Some MIDI controllers may overflow if you send too much data. Probably not a concern with two channels sent - but, in general, something to think about.

The "official" way (using Zone Control):

1) Place MODX7 in multi-channel MIDI mode (this is MODX's factory initialization default). [UTILITY] then “Settings” -> “Advanced” - MIDI I/O mode parameter
2) Recall a single-PART bass guitar Performance. Most bass guitars in MODX are single-PART - so this isn't much of a limitation on your choices. This will, by definition, place the bass guitar on PART 1. PART 1 in multi-channel MIDI mode will transmit on MIDI Channel 1. Note: search for the bass guitar should use [CATEGORY SEARCH] and you can filter by single-PART Performances and then choose the bass category and appropriate sub-category if desired
3) From [PERFORMANCE] (HOME), press the [+] button to add PART 2 and choose any single-PART organ part. It doesn't matter which one you choose. I say to pick organ only so the screen can show "organ" as a reference. We'll configure PART 2 not to trigger the internal tone generator so it is external only. By definition, PART 2 will transmit on MIDI Channel 2
4) ... and here's the start of differences - First, make sure Zone Master mode is turned on. Press [UTILITY] then "Settings" -> "Advanced" and make sure "Zone Master" is ON.
5) Then edit PART 2, select "Common" (at bottom of screen) instead of any of the elements. Then choose the "Part Settings" -> "Zone Settings" menu. From here, turn "Zone" ON (if OFF - you will not see all the options). Turn "Int SW" OFF - which shuts off this PART's internal sounds. Make sure the transmit channel is set to "2". Note that zone control allows your MIDI transmit channel to assume any value and does not need to match the current PART number.
6) Edit PART 1, select "Common". Choose "Part Settings" -> "Zone Settings" menu. Turn "Zone" ON. Turn "Int SW" ON (we want PART 1 - the bass to sound using the internal tone generator). Set the transmit channel to "OFF". This will make sure PART 1 does not transmit any MIDI. I'm not sure you have this as a requirement or not - but I am assuming not transmitting the bass on MIDI is just as good (or better) than transmitting the data on channel 1.

Zone control affords you other control over the PARTs and what is sent or filtered from these PARTs. You can dig more into those options:

https://yamahasynth.com/montage-category/montage-midi-zone-master-faq

There may be a MODX version, but I couldn't quickly dig it up. MODX is similar/same in function.

Hi Jim! How’ve you been?
Anytime you want to configure your MODX to communicate via MIDI, use the ZONE MASTER feature. Once activated you can create a custom MIDI configuration for each Performance.

You can, when controlling your external keyboard via MIDI, route the audio of that keyboard into the A/D In of the MODX. The advantage here is that you can preset all volumes, effects, and behavior of the external synth as if it were a Part of the MODX’s Motion Control Synthesis Engine. You can even use it as a modulation source. (Of course, this depends on what you are doing with its audio output... but it’s an option).

You will be able to balance volume, create splits/layers with internal sounds, apply a set of MODX dual Insertion Effects, add Reverb, Variation Effect Sends, and evening “morph” to it same as if it were an internal MODX Part.

Zone Master will let you determine what each Performance slot is doing... including dedicating a slot for your external device.
The Audio In option, if you choose to use it, will allow you Control the actual audio from that device... and apply effects, etc.

Instead of a separate MASTER mode (as in the past) the Master Keyboard functions have been rolled up and placed within each Performance. Instead of just 128 setups you can have access to 640 in the User Bank (one per each Performance) and times 8 if you count the Library locations.

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