You have to bypass the OEM amp if you install new speakers? Why? YOu cant use the amp with aftermarket speakers?

 

If I'm following this right, (I have my stock speakers and amp sitting right in front of me) the rear speakers have little microphones on them (right on the harness plug). These microphones measure distortion and adjust the rear amp accordingly. Distortion is dc, and not only does it sound bad, but it can fry the outputs or the speaker. So the microphones are part of the circuit that runs the rear speakers. If the micropone circuit senses any distortion, they can then send a signal to adjust the rear amp accordingly. If they are not present in the circuit, you will have no audio going to the speakers. In other words, the rear speakers and amp are one big loop, with the only external intrusion into the circuit is signal and power. Signal comes into the AFS amp and out to the speakers, while the mics monitor for clipping. When the mic senses clipping, the AFS amp cuts down the output untill clipping is no longer present.