Drum Voice

I've added the following to the docs for setting a voice in a drum track to the manual: 

All DRUM tracks share a common MIDI channel. This, for all practical purposes, means that all DRUM tracks will have the same VOICE or "drum kit''. In most cases, it is recommended that you use the VOICE command only in the generic track "Drum''. At this point, MMA doesn't enforce this recommendation. 

Hopefully this will eliminate some confusion.