a lot going on here. There are a couple of ways to do this:
Amplifier: 5ch + 4 ch, or 8 ch + 1 ch
I do not know of a 9 channel amplifer
The 8 channel amplifier (JL audio) above is a class d, which is less than ideal compared to a class AB or true Class A amplifier . so that said, I would go with a 5ch + 4ch
Speakers: you have already chosen Memphis drivers
Sound processor and DTA: in my opinion, its the only way to do this the right way. You don't HAVE to use a sound processor, but when you are spending money on a system, you may as well do it right. There are a number to choose from (JL Twk 88, Rockford 360.3, hertx H8, Audison Bitone). I personally have the bitone in my CTS-V and the H8 in my Camaro
Connection: imo, the best method to connect your factory headunit , to DSP, to amplifiers is with the NAV-TV’s M650-GM processor.
https://navtv.com/products/NTV-KIT838/m650-gm.html
Will allow you to maintain all factory sounds, door chimes, onstar, and back up warnings etc (at a normal volume) without removing OEM door microphones. The only thing you loose is on the fly control front to rear fade. But if you are setting up a perfect system you shouldn't need it.
I just finished a similar upgrade on my Camaro
http://www.camaro6.com/forums/showthread.php?t=513195 with many of the above components.
I don't have rear deck speakers and am running a 2 way setup up front (tweeter and midbass passive) and one subwoofer for a simple 7 speaker setup. But I may add two more speakers up front for a 3 way setup, running the tweets and midranges passive together, then woofers active, rear fill and sub active as well. This is a quasi-3 way front stage, but sounds great in my CTS-V.