I did not read everything but the most important points to make.
1. You need an amplifier for your speakers, subwoofer or not. This could not be more over stated. Everything without one sounds like shit no matter what you spend on a head unit.
2. Throw away the rear speakers. All that they are good for is causing canceling waves. Trust me, just play with the stock one, fader to front, you might turn the volume up more, but you will notice how much more clear everything sounds.
3. A good install, sound deadening is good, things well mounted, things wired properly so you do not get noise etc...
If you do those two things then just buy nice stuff (haha easier said than done). A good head unit is key for a good DAC. Good amps are very important, speakers you actually can go semi inexpensive on and get nice sound.