The only multi-I/O VSTi i'm using is the Korg M1 (and WaveStation i guess). I've never routed audio out to different channels and wondered what good your changes would do. IOW, what audio capabilities should we now have if we have multi-out VSTs?
BTW, there should be a logging feature in MPT, accessible via menu (maybe the Help menu), so we can track behaviors and code execution. I use the log in UnrealEdit, for example, to figure out what i'm doing wrong, or what was or wasn't done when i thought i was doing something.