If you want to really cheat and make it sound good here is a couple of things we have done from time to time and the results were awesome. Keep the factory amp and headunit functioning. Cut the wires coming out of the amp out to the speakers, Put a set of PAC lineout converters on that set of wires and then your RCA's and install a high quality four channel amp. Then turn right back around and run the outputs from the amplifier to the OEM wires that are heading to the OEM speakers where you cut the wires in half to install the line out converters. The wires heading up to the OEM sub are blue,blue/black, green,green black. Cut the wires to disable the oem sub and install a LOC on the half of the wires coming from the amp and then you can install your sub, and sub amp. The OEM bose speakers actually sound really good when they have an amp that can give them lots of clean power, the subs also sound really good when done this way. The part of it that I like is that it will not run out of volume like it does when the oem amp is powering the speakers and you retain 100% OEM look and function of all related components, RSA steering wheel controls, onstar etc. We have done it on more than one and all have been pleased with the results