So, I got the deck installed yesterday.. I have installed many head units in the past, but this one took a lot longer than expected. I was not aware that the amp in the car was a 4 channel amp and that all speakers where driven from it.
For anyone who is planning on doing this, there are two connections in the back of the radio. One supplies power to the radio and the other is an 8 pin round connector that sends all signals to the amp (remote power wire to turn on the amp, speaker signal wires, speaker grounds). There are a two pairs of 3 wires, one for the front speakers and one for the back speakers. Each pair consists of a left channel, right channel, and a ground. The easiest way to connect these to the new deck is to splice in RCA cables for the front and rear. Use the common ground for both left and right channels when splicing in. You will not use any of the speaker wires provided in the new head unit, only the RCA connections since all speakers are running from the factory amp.
The new head unit made a big difference in sound quality already, even running on the factory speakers. I will install the new speakers tonight and update again.
Kevin