Sorry if you have done this, but are you hard panning the things you want to assign?
So,
Kick output 1+2 panned hard left
Snare Output 1+2 hard right
Toms output 3+4 Hard Left
Cymbals 3+4 hard right?
So,
Kick output 1+2 panned hard left
Snare Output 1+2 hard right
Toms output 3+4 Hard Left
Cymbals 3+4 hard right?