what you think I should change or do?

I am having a friend help me build up my stereo, this is what I have so far...
Boston acoustics fx6's
2 620LF woofers
2Neo 3r tweeters
2 620X crossover networks
The head unit is an alpine CDE-7872
the very rear speakers arent working.
I was planning on adding a jl stealth box with the 300watt sub with an amp off ebay or something. Curious how much some of you paid for this.
I was also planning on dynamatting or brownbreading my floorpan, and dunno but curious about replacing the stock very rear speakers with 6x9's and run them off an amp but dunno what kind to get and if thats really worth while.
I listen to hard rock so I dont need it to thump TOO hard but I do want some bass and really clear nice sound and the ability to play LOUD without distorting too much and it to be able to play fast with out popping and stuff.... just like to get some opinions from some people who have done it before thanks!

Forget the 6x9's in the back idea. The flimsy plastic panel doesn't have enough mass to keep from vibrating like hell when he speaker plays. Besides, if you do your front stage right you won't need ANY rear speakers.

Yeah my friend said to leave the rears not working or remove them... thanks, oh and are those boston acoustics speakers pretty good thats what a couple people told me, they came with the car by the way...

I'm using a set of BA Rally Series components now. They replaced the Infinity Reference Series I had before. The Infinity midwoofers couldn't handle loud midbass without distorting badly. And that was with them high passed at 80Hz @ 18dB/octave. The Bostons sound much better.