Hi there,
I´m going to give you a good reason why you don´t get output from your drum kit......
It happened to me once, and I believe you when you say you´d tried it all....
It´s a very basic problem that we usually don´t remember or don´t assume is happening.
Well then enough said......
Assuming your inputting your drums into 2 different channels and setting the output in stereo....
If so, Your problem is that these channels are OUT OF FASE within each other.
And if this is not the case, then check the cables used to connect the drum kit to see if they are wired out of fase within each other.
I could give you an explanation to what happens when you OUT PHASE a drum kit, but I guess you can figure this out yourself if this advice solves your problem.
Please let us know if this advice helped
May God bless you