Thanks for the advice and comments, HPMAN. Time to dig in:

HPMAN (./2) :
I believe the only good solution comes with writing a proper tracker. I wouldn't pursue with MVStracker and its z80 emulation approach tho.

That's what I figured. There's only so much you can do without rewriting the entire thing from scratch.

HPMAN (./2) :
In a nutshell you want to import and run the mame 2610 core in your application, then you can simply play instruments by writing to its ports.

Simple enough; this was the one part of MVSTracker that I knew worked, even after my hacks, and even with older code. Main issue here is working around MAME's device system... maybe I can get lucky and find an older version before the conversion to devices or something.

I've been hammering away at a skeleton of a tracker in C# with WinForms for a bit, but it's nowhere near complete. Most of the work is being done in the back-end, preparing the required data structures and routines. I'm not sure if anyone would like to help with the project, but I'm making a public note of it just in case.