I don't know any more off-hand, all I can suggest is checking out the ScummC documentation on iMUSE, since it lists some of the SysEx commands used in SCUMM V6. Unfortunately, the ScummC site seems to be down, the best link I can provide is the one below, which may not have the latest info:
(As an aside, would you mind adding your discoveries to the ScummVM wiki? That way other people can build on your work, and there's less chance of the info disappearing like the ScummC pages.
I'd suggest putting it either in the "Sound Resources" page, or creating a new one for iMUSE stuff)