First off, I should mention that I'm using DP 4 and MMV in a classroom situation. So, part of my goals is to be able to set things up and explain things in a manner that is understandable by my students (college, but not quite experienced).
Now, if I call up one MMV "instrument" and feed to it a MIDI stream, it works perfectly fine. If I want to have a different sound, I apparently need to use a new MMV "instrument" (not track), unless I'm doing something wrong. If I do open a new instrument, I can get different sounds, but the program stutters and often freezes.
Curiously, if I do use the patch column, I do get a patch change. I just can't identify the patch unless I go to MMV and see - it's somewhat "peck and find". I haven't tried it with two different MIDI tracks going in to the same instrument.
So, my goal would be to have one MMV 'instrument' and several MIDI tracks running into it.
Conversely, I could have my students convert each track to audio after it's recorded in MIDI. But then, I'm back in the late-70s...