Brutal669x

Hello, I recently purchased a 2008 Hummer H3 Lux equipped with the Monsoon "premium" audio package (front doors 6.5 components,rear doors 6.5 mids, 8 inch sub , factory amp 25w x4, 100 w to the sub). The system doesnt actually sound bad, but I grown accustom to using android auto. My head is overloaded with facts and figures from across the web. Ive spent many hours researching over the last 3weeks on Crutchfield , Youtube videos and maunfactures websites. I am not super knowledgable acr audio wise, all I state in this thread im just repeating .Everything Ive discovered thus far states that If I replace my head unit,then Ill also need to replace every speaker in the Hummer. I have (2) head units, a Pioneer AVH4800BS (CD/DVD), and a Kenwood DMX7709s (Android auto). Ive purchased the proper PAC (RP5-GM11) which is supposed to retain your factory amps/speakers/etc, but this is also where the frustration begins. I also own (2) amps and boxed 12inch subs with a neocap5. Id like to keep the small amount of cargo space the Hummer has, if I install my 12s, which require 1.6 ft3 per sub, that space is gone. The amps seem like they are way too overpowered to use with anything anything thats not competion level. I have a 1 ohm stable Hypnotic HYP2800d monoblock 2800 watts@ 1ohm, 1400 watts@ 2ohm. My second Amp is a Quantum QPX 2800.4 3600 watt 4 channel. I have no idea what the RMS per channel is for the quantum.The stats for it arent very clear. They refer Dynamic power handling which Ive read is not an accurate estimation . Im not sure how much speaker I need in order to use that amp. I know I need (4) 6.5s but at what RMS rating. Then there is the factory sub..how do I go about replacing that ? I know JLAudio makes a Stealth box...but im not spending $900 bucks on one speaker that ill still need an amp to run .. Suggestions/advice on either how to use what I have, or a new approach or brands to look into is greatly appreciated. I mainly listen to metal , EDM and occassionally some hip hop. Cargo space is appr. 42" wide x 35" deep.