Need some help from some pros on what to do here.

I have a 14 Jeep Grand Cherokee SRT with the Harmon Kardon system, but it sucks ***** so im changing it out but dont know how to do what I want, with retaining the factory amp for the stock speakers and sub.

The stock HK system consists of 13 speakers and 1 sub:
1 mid in the center dash. 1 tweeter in each front door, 1 mid in each front door, 1 woofer in each front door.
1 tweeter in each rear door
1 woofer in each rear door.
1 mid in each rear d-pillar
10" sub in liftgate
825w 11 channel (all active) class d amp with logic 7 processing
HK says its a "7.3 Surround Sound System"

Anyway, I have all Hertz Mille component speakers:
2 Hertz ML 280.3 Legend Tweeters for the front A-Pillars
2 Hertz ML 700.3 Legend Midrange for the front doors
2 Hertz ML 1650.3 Legend Woofers for the front doors
2 Hertz ML 280 Tweeters for the rear doors
2 Hertz ML 1600 Woofers for the rear doors.

I'm debating on switching the stock 3.5 Mids in the center dash and the 2 in the rear d-pillars, but havent made a decision yet.
Not going to upgrade the subwoofer just yet, but will soon.

So that leaves me with 3 stock mids and 1 stock sub and 8 Hertz.

But im stuck on where to begin. I would like to run the 2 front doors active and the 2 rear doors passive, which would mean I need a DSP. So im not sure how I would get a DSP to handle all the Hertz speakers and the stock ones.

Can I leave the stock amp to power the stock speakers and sub, as well as install my own DSP, amps and speakers?
Would I need more than one DSP to do what I want, and would you recommend 2 4channel amps, or 1 8channel amp?

Or do I have to remove the stock amp altogether and get another amp/dsp to control the stock speakers with the Hertz?

Anyone with any advice, please share. Ill take anything lol.

(PAC Audio is about to release a harness which will enable me to run RCAs/TOSLINK out of my stock UConnect head unit, thank god because I have no desire to change out it out and do not want to splice any wires)