Jason,

Your install might be similar to my 2002 Benz install, connecting the empeg (and an Alpine, via a source switch) to the stock Bose amp and speakers. I wound up using a Metra harness for a VW, but that's beside the point. Or is your stock amp a Bose, because I've read plenty of good, bad, and ugly information about them.

You may need an OEM Interface adapter to convert line out RCAs to the proper input for your amp. I have a Peripheral Super VEN 4 sitting on my desk but haven't tried it yet.

Honestly, it sounds like you need an amp between the empeg and your stock amp. How else can you give speaker level inputs to your stock amp? Using two amps seems silly. Maybe you've got some uninformed information about your stock amp.

For the Mercedes Bose, which is apparently similar to VW, people claim to hook up speaker level inputs and it works fine. Turn the volume up even slightly and it becomes overdriven since it's double amplified. Other people claim to hook up line level inputs (which I did) and it works fine. But turning the volume to full blast is only kind of loud because the signal isn't strong enough. Apparently the Bose amp expects 4V balanced line input; not speaker level and not 2V RCA line level. The SVEN 4 can apparently convert from speaker or line level to the proper 4V balanced.

I hope this helps.