If you are just looking to upgrade the head unit and mabe the speakers, there is an easy trick you can do. You can bypass the rear amp by joining the rear speaker inputs to the outputs. The amp is a little black box mounted under the back deck. Right next to the seat back fold down lock. Just follow the wires back from the speakers to the box, but make sure you are following the wires to the speakers and not the Accoustic Feedback System (the little microphone and circuit mounted on the speaker itself). You can leave the power to the amp connected, since it will only turn on with the factory head unit. The door speakers are 6.5's with 1" tweeters by the door handle. I suggest getting a matched speaker pair with a passive crossover between the tweeter and 6.5" mid range. Running speaker wire through the doors is impossible, since all the factory wiring is harnessed through the door gromets. I just tapped my speaker wire at the head unit end, then connected the crossovers from the main factory speaker wire in the door.