Ok, from what I understand about the factory amplified system is that only the rear speakers go through the amp, and the door speakers are powered by the radio. When changing the radio, you will never get the rear speakers to sound the same unless you have a low-pass crossover in the radio for the rear speakers. The factory amp does not have it built in, it is in the radios outputs. The best thing to do in the crossfire is replace the radio, by-pass the factory amp, and replace the rear speakers wit ha set of full range speakers. You may loose a bit of bass, but you will have better clarity and volume. If you keep the factory amp, you can adjust the levels of the rear speakers going to the amp with the converther until it is at the proper levels.