I installed a pioneer head unit about 2 weeks ago and you can view my thread here. http://www.xoutpost.com/electronics/...tall-pics.html

The Speaker wires are definitely in the back right off the harness on the factory amp. The OEM Amp has built in crossovers for each speaker. You will send all frequencies to all the speakers and will cause more distortion and eventually may break the speakers.

Your installer may need to find the high input wires for the factory amp to feed it the audio signals OR feed the speaker outputs of the Avic to the speakers wires but you have to install a passive crossover for each door. I did not connect the dash speakers on mine.

I would prefer to remove the OEM amp since the Pioneer headunit is pretty powerful by itself.

A small concern I may have for you when using the Pioneer speaker output is the fuse on the OEM radio. It is only 7.5A. The pioneer uses a 10A fuse so if you listen loud then there is a chance it may blow the OEM fuse.

PM me if you need more information.