I posted over in the Installation Notes section here, but didn't mention my problems.

First, there is engine noise. Second, with the engine off, I still have feedback. My guess is it has something to do with the empeg's outputs being 4V; I don't think the AUX IN of the cd player can handle that (especially when they've all been merged to connect to a single 1/8" stereo plug).

Keep in mind this is temporary. Not too far in the future there will be a new cd player, and an amplifier. If I can solve these problems easily; great. If not, I'll just keep the volume down until I have the new components.