Maybe its not possible, but shouldnt it be easy to just hook up the line livel of the stock head unit to the aux in of the empeg and then use the factory amp for driving the speakers. Is it connect the empeg to the factory amp?
About the speaker wiring, arent they just wired to the factory amp. Please tell me if this is possible at all.. I know quite a bit about home stereos, but when it comes to car stereos, Im quite clueless.