Hello Ryan

> I had already identified the distortion on the handclap/tambourine channel. I plugged a cable into that out and voila! The main outs are clean now.
>
> So.... where do I go from here

Now check (without the cable in the single out) whether moving the fader
of the handclap/tambourine channel does change the behaviour.

My main suspect is this fader. Inspect it and clean it (unsolder, open
the clamps of the housing, clean it with a q-tip and Caigs Faderlube 5,
remount the housing, resolder it).

The second thought goes to the Dual-OpAmp IC204 on the mixer board.
Either it is broken or shortend by some thing (too much solder Metal
flake ). But this dual opamp is used also for the hihat, so it would
mean that only one of the two opamps in this chip is broke.
The Opamp is a M5218L (SIL-Version). As far as I know it is no longer
produced but still available at most electronics suppliers.

Florian