I know a bit about the N800's audio jack. But knowing nothing about electronic drumsets, I don't know what cable either...

See Nokia's docs on the cable for info; audio out is compatible with a standard 3.5mm jack, with the mic (of course, there's no video output) on the extra ring. (I'm assuming that "mix in" means an input to the drum set? If you need the mic access, get a splitter from EPO, but the tablets don't record well...)