I actually just use a microphone on my bass drum directly into the line in and just train it as a single zone. After messing with the input settings it works 100%.
I also have an ancient Roland pad with a trs line out that I sometimes use as a single zone tom. It also works perfectly.
Now that I have maxed out the inputs with the cymbals, I am able to get a 9-piece kit set up like this:
Sensory triggers x4: snare, tom 1, tom 2, floor tom
Line in mic used as a bass drum trigger.
Cymbal sensors for the hats, crash, ride.
A second mic to pick up the physical sound of the 18” evans db one cymbal that was left over. With some eq it sounds…. Not bad.