Well, I just came in from chasing wires all evening and I think I have it figured out. Man that FSM can be confusing at times. Anyway, after pulling the back end apart and chasing connectors, I located the 20P Gray connector running down to the amp (this is not to be confused with the 20P Gray connector on the back of the audio unit since the wire colors don't match ). Anyway, now that the preamp signal wires have been located, I will try to identify the best place to tap/splice into said wires and get the signal routed down to the new amp. Im going to study the schematics a little more but I may just disconnect the whole factory amp to eliminate unnecessary drain on the electrical system. I will first need to confirm nothing necessary routes through for any other purpose.