OK. I have an answer, but I have an XP-80. You can assign any part to any track. So, if you record some drums on track 10, but you want to put your congas on track 11, you just select track 11, but select part 10. So, MIDI channel 10 is now playing on 2 separate tracks.
I think about things in terms of position rather than by name, because I'm blind and need to know how many times to push the arrows and such. Anyway, I think it is the very last thing on the sequencer screen. I get to it by pressing up arrow from the point where you can select what song you want the seq to play. Pressing up from the top will take you to the bottom right I think. Hope that helped more than it confused.