OK, for that, you will want to pull both the factory head unit and the factory amp. The trunk is the only place in which both the speaker wiring and the head unit wiring coexist. So, you would just splice the head unit wiring over to the speaker wiring and then the head unit would be directly powering the speakers. But, you would need to add some active passovers in the splices:
Your car has 10 speakers, and these are all direct runs from the speakers to the factory amp. In a normal aftermarket stereo installation, you typically see direct runs per channel, and then some kind of passive crossover at the speaker locations to separate the lows, mids, and highs. The factory system does not have any passive crossovers, so you would need to add them. These are the speaker locations and functions:
- 2 front door tweeters
- 2 front door midrange speakers
- 2 front door woofer speakers
- 2 back door tweeters
- 2 back door woofer speakers
So, to bypass both the factory head unit and the factory amp, you would need to add a three-way passive crossover for the front door speakers, and you would need to add a two-way passive crossover for the back door speakers. It is hard to buy an aftermarket crossover that is tuned to your existing speakers. So, it might be a lot easier to just buy new speakers that come with passive crossovers (like the Bavarian Soundwerks kits), and replace your speakers along with the new head unit.