My first thought: Your making sort of a sideways move.
The equipment your listing is good, but not so much better than the stock system that it is worth the considerable effort needed to make it work.
Do you listen to rock really loud? or are you a bass pig loving techno at 110db? Or something different all-together?
You obviously know your forums, I suggest
diyma and start reading. Your best bet I think is to go to a local shop and listen, everyone's ears are different. A tweeter someone might like you could find harsh, plus you need to define what type of listener you are. This market is killer for audio shops, they are getting no work, I bet you can haggle and get a good deal there right now.
I'll just put what I've decided, my stuff:
Eclipse AVN-6620
Front: CDT HD-62 + Upstage kit (4 front tweeters)
Rear: CDT EF-61
Amps: Alpine PDX 4x150 + PDX 1.600
Sub: Stereo Integrity SI Mag D2 V4 (whenver it gets here)
Plus a whole lot of Second Skin sound deadening. I honestly still just have a pile of equipment (I'm waiting to install the speakers + amps till I recieve the sub).
The place where you will get the best bang for you buck is imo the instalation if you sound deaden enough you can make any speaker sound really good.
Check out these company for subs: SSA, Image Dynamics, JL Audio, Digital Designs ... there is a lot out there that is really good but Crutchfield doesn't carry.
