DescentBB

How would I choose a different track for my level (in signature) because I don't to use the grating d2 l1 music
I'm thinking of using the d1 PlayStation track called 'rusty'

For non-MIDI there isn't much you can do, at least in terms of vanilla support. As for MIDI, all you need to do is either find (in the case of anything built into D1 or D2, where it would be in the respective .HOG) or convert your midi (MIDI2HMP or DTX2) to a .HMP file.

For non-midi I can't quite remember off the top of my head how we did it but take a look at how it's set up in Cererian Expedition. If you manage to get it set up that way it will work with both Rebirth and D2X-XL, although there's no way to make custom streaming music work on DOS.