This is possible yes. You can have 8 MIDI tracks and 8 Audio Tracks on the Play for 16 total.
The MIDI tracks are not channel locked, but can be set per step. So you could set track 2 to USB 1 and track 2 to USB 2, which is what I usually do for organization but you could have track 1 triggering USB 1 on some steps and USB 2 on others. There is a lot of flexibility with MIDI here.