Fluffy : LA products aren't really known for the SQ, unless you're going for SPL la. You're better off going for Alpine type-X or DLS components or even Peerless. There's this dude Xcheong who's selling them at bargain prices! Go look for him in the buy/sell section.
Btw, if I were you, I'd throw the back speakers and just use front comp (2-way) and 1 sub. Then your setup would be easier to play with. use a monoblock for your sub and use a good 2-channel amp (or 4 channel if you wanna bridge) and pump in 100 RMS watts in the front. If you position the tweeters properly and all, it'll fill the rear nicely too without back speakers. Trust me on this.. :) Ask unker soong (pisces23) to let you listen to his front comp+sub+2 amp setup and you'll understand what I mean. But of course, unker soong is one of those gila ICE people, just don't kena poison too much after listening to his setup :D
With the right tuning, the mid, tweet and even bass sounds can be projected to fill in the front (yes.. even the bass!) to make the sound very nice.
Also, good amps matter as well, don't use the HU built in amp if possible you wouldn't want to kill the HU in the long run!
Do what I am doing :
Front : Alpine Type-S comp set
Back : 12" sub
Amps : feed 75 RMS to front comp set and one 300 RMS monoblock to sub.
This cost me a little more than RM1100 cuz all 2nd hand. But I'm bloody happy it does the job of filling the back as well as the front very well. Looking to upgrade liao.. to 5.1 surround sound! Haha