You have MIDI through from your Kronos so MODX will see all messages the Kronos does. This isn't necessarily a good thing since for MSB/LSB/PC - Kronos and MODX will have different interpretations of these messages and possibly conflict when both see the same message. Conflict meaning MODX sees a PC for Kronos and does the wrong thing - or Kronos sees a PC for MODX and does the wrong thing.

As a for-instance: if you wanted to target Kronos' INT-A, Program # 36 then MSB=0, LSB=0, PC=36 for this target. If MODX sees this, it will change to a GM Voice #36 - which is most likely not what you want.

It's unlikely you will target MSB=0, LSB=0 for MODX's GM Voices (intentionally changing to MODX GM Voices) - so the reverse conflict is unlikely. However, what happens when an unsupported MSB/LSB/PC is issued is unknown with Kronos. I believe MODX would ignore a PC if the MSB/LSB was not supported although I have not tested this recently.

When sending PCs to MODX - be sure to precede the PC with an MSB/LSB pair that matches what you're trying to do. Most often, you'll be wanting to change the Performance to something else. If so, follow the table in the data list for "Performance (Multi Part) " (MSB=64) and be sure the LSB matches what you're trying to change (0-31 for presets, 32-36 for user, 40-79 for library).

If you have the Performance recalled that you want to switch to, you can press [PERFORMANCE] (HOME), then touch the Performance name at the top of the touchscreen, then choose "Property" from the popup window. You'll see a summary of the MSB/LSB/PC needed to recall this Performance. Like you discovered with Kronos - keep in mind that sometimes software or keyboards do not agree with the PC numbering. Some start the number system at 0 (0-127) and some start at 1 (1-128). This is what causes that one-PC value offset you experienced with Kronos and may run into the same with MODX.

... you're probably using the audio interface because either it has more physical I/Os than MODX (more than 2 ins, for example) or you like the sound/quality of the audio interface you're using vs. MODX. That said - if the audio interface isn't "buying" you anything - then an alternative setup would help to split the MIDI messages so Kronos and MODX see their own stream and do not share - unless your PC forwards messages (unless you want them to see each other). And this forwarding can be selective/filtered such that MSB/LSB/PC messages do not forward which would avoid possible conflicts.

The configuration would be MODX USB Host port to the PC. Kronos 5-pin MIDI IN to MODX 5-pin MIDI OUT, Kronos 5-pin MIDI OUT to MODX 5-pin MIDI IN.

To target the Kronos from your DAW, you would send MIDI to the MODX-3 port (port 3). MODX itself would not see these messages so you could send MSB/LSB/PC to Kronos without conflicts. To target MODX from your DAW, you would send MIDI to the MODX-1 port (port 1). Likewise, sending MSB/LSB/PC messages to MODX would not be seen by Kronos avoiding any possible conflicts.