Hey Martin, sorry I took so long to respond. I've been busy with school.
The answer to this is very easy. The answer is - yes and yes.
As someone here already said, you could easily change the MIDI CHANNEL of many tracks to 10 and use each track for a different drum waveform. The only deal is that they will all be using the same drum set (no changing drum sets, doing so will change the rhythm set on all other tracks).
Since you would have recorded differnt source waveforms to different tracks, you could then use the PALLETTE SLIDERS or the DATA WHEEL to change the volume of each individual drum key.
This method is great, but you just have to be very careful when you do track edits. Aftertouch would still affect the whole drum patch.
The other way to do this is to make a MENU patch in which a regular patch could be a bass drum. Another one could be a snare drum. You would then assign all of these patches to different parts in a performance. This way is a little more flexible. You could easily use the TONE COPY funciton to copy a drum waveform in a rhythm set to a TONE in a PATCH.
This way is cool, but time consuming. It would also waste parts in a performance. The cool thing about this is however, that polyphony would be at a minimum, you don't have to worry about drums being confined to PART 10 and you would have
complete control.
The Infamous EPU.