The output of the factory stereo isn't at 4v to the factory amp, it's more like 400mv. This prevents us from switching between the factory stereo and empeg-car on the input side of the amplifier.

Are you sure about that? One of Tony's FAQs (here) suggests that this may not really be an issue... or am I misunderstanding the problem? Probably... the nuts and bolts and wires end of this audio stuff is not my strong suit. I did ask my installer about your problem yesterday, though, and he suggested resistors on the plus side of the empeg outputs to bring the voltages down to something your amplifier would be happy with. He cautioned against using small (physical size) resistors, said you would need something big enough to dissipate a fair bit of heat.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"