This is for the Infinity equipped cars only.
You CAN NOT replace the factory amp while keeping the stock speakers with just an aftermarket amp. The factory amplifier performs all crossovers, time alignment, equalization, and amplification for 11 separate channels. Also, the head unit sends the signal to the factory amplifier in optical form.
To properly replace the factory amplifier with anything else in the infinity system, while keeping the stock speakers, you would need, at minimum, TWO Alpine H800 processors, and THREE 4 channel amps. This gives you one extra channel, but that is the best way to do it. That gives one channel per voice coil on the subwoofer, one channel per rear door speaker, one channel per front door speaker, one channel for the center speaker, and TWO channels for the front left and right midrange/tweeters. You would need to daisy chain the processors together. And they do HAVE to be that specific processor, as it is the only processor that does a proper center channel and proper rear fill.
Obviously all of that is a lot of work, so one might ask, is it worth it? It depends. There is a guy whose girlfriend has a Lexus SUV with a premium BOSE system. I judged said system at a sound quality competition, and IIRC it scored around the high 60's. After that show, the guy took the signal from the head unit, ran it to a dedicated processor, bypassed the stock processor, and used the stock BOSE amplifier with his own tune. That car now scores a solid 80. For reference, that is a completely stock car with just tuning on stock amp and speakers that scores 5 points away from the top Modex and Extreme class cars, the latter of which can do absolutely anything to the car they want.
You CAN NOT replace the factory amp while keeping the stock speakers with just an aftermarket amp. The factory amplifier performs all crossovers, time alignment, equalization, and amplification for 11 separate channels. Also, the head unit sends the signal to the factory amplifier in optical form.
To properly replace the factory amplifier with anything else in the infinity system, while keeping the stock speakers, you would need, at minimum, TWO Alpine H800 processors, and THREE 4 channel amps. This gives you one extra channel, but that is the best way to do it. That gives one channel per voice coil on the subwoofer, one channel per rear door speaker, one channel per front door speaker, one channel for the center speaker, and TWO channels for the front left and right midrange/tweeters. You would need to daisy chain the processors together. And they do HAVE to be that specific processor, as it is the only processor that does a proper center channel and proper rear fill.
Obviously all of that is a lot of work, so one might ask, is it worth it? It depends. There is a guy whose girlfriend has a Lexus SUV with a premium BOSE system. I judged said system at a sound quality competition, and IIRC it scored around the high 60's. After that show, the guy took the signal from the head unit, ran it to a dedicated processor, bypassed the stock processor, and used the stock BOSE amplifier with his own tune. That car now scores a solid 80. For reference, that is a completely stock car with just tuning on stock amp and speakers that scores 5 points away from the top Modex and Extreme class cars, the latter of which can do absolutely anything to the car they want.
