So I've been doing a little research on aftermarket amp and speaker installs that keep the factory head unit and here's what I'm planning to buy:

Speakers:
Front - Polk Audio DB5251 5.25-Inch 2-Way Component
Back - Polk Audio DB651s Slim-Mount 6.5-Inch
Sub - Polk Audio db1040DVC

Amps:
Speakers - rockford fosgate pbr300x4
Sub - Polk Audio Pa880 Monoblock 800w

I'm mostly curious if anyone has used that "plug and play" Rockford amp and had any success with it. Supposedly it's small enough to fit in place of the factory amp and I like the idea of keeping all the factory speaker wiring in place, aside from the sub. I'm fine with ditching the center channel if it will make things easier.

 

I've got the PnP amp. Fits and works well. Been running it for 3 years now and no issues.