My ’03 Silverado stereo system

Hey everybody,

I am new to post in the forum but I have been reading you guys for a while and found that you are very helpful.  I would like any opinions on my stereo equipment and if any of you think I should change anything to make it sound better.  I am looking for mostly SPL, but I would like some good SQ too.

Here's the basic system:

'03 Chevrolet Silverado, Extended Cab 5.3L

HU: Alpine 7894 mp3/cd player

Subwoofers: 2 JL12W3v2 dual 2 ohm (running at 2 ohms total)

Subwoofer Amplifier: Rockford Fosgate 500bd mono (500Watts at 2 ohms)

I just bought all my highs and I will be installing them this weekend on an amp and crossover that I got about 5 years ago pretty cheap.

Speakers: Front doors are Kenwood KFC1789ie 6-3/4", Rear doors are Kenwood KFC4675 4X6"

Speaker Amplifier: Prestige PA-250 running 2 channels at 2 ohms each, 50 W each (I am pretty sure this is the weak link of the system, but like I said it is am amp I had laying around, and that doesn't cost anything!

Crossover: Profile QX11 running to highs and subs

I have a downfire box under the backseat for the 12's with some pillow stuffing in there to trick the speaker into acting like the box is bigger.  I just installed a 145 amp alternator from a Tahoe so I could decrease the light blinking from bass hits.  It definitely helped out, but still blinks a little.  Like I said, I will be tearing into the truck this weekend, so if there is any advice or opinions or anything you guys think, I would really appreciate it.  I know a lot of you guys are professions so your opinions are usually pretty accurate.  Sorry for the long post and thanks for any help you give.