Avast Thar Mateys,
Setting up crossfades on a TD-12 should be very similar to the TD-20, which is what the old Pyrate uses. The issue is that Roland does not always use sequential midi note numbers for various instruments. For example, if you wanted a crossfade on a snare drum to go from brushes to a light snare hit to a heavy snare to a rimshot, the midi note numbers may not be sequential as required by the zendrum firmware. Also, the midi notes that Rolnad does use are limited and do not include all 127 midi notes. However, at least on the TD-20, you can edit instrument parameters for any given acceptable midi note number. Therefore, even though you may program a 4 note sequence equating to a snare dum, gong, kick and ride cymbal, you can edit the sounds using the instrument edit feature of the Roland. I have done this to get a triangle sound from what would otherwise be a tom midi. The only precaution is that if you program any other pad to that specific midi note number, it will retain the edited sound. So if you want that ride cymbal that you just made part of your crossfade sequence, you have to use a different midi note number.
I hope all this helps. It is not as difficult as it sounds.
Fair Winds and Following Seas,