I would invest in rear speakers, but don't use as much power when you run them (for example, run them off your deck power and run the fronts with an amp). Also, you can do what I do which is use a 6 1/2 midbass for rear fill. It won't produce highs that could take away from your front soundstage, but provide you with rear fill.

Michael

 

Your project is actually a neat idea, SQ for a modest investment. First off, the head deck is fine sounding, many folks here are strong into Pioneer, but the most recent Alpine hardware is very good, not propriatary, and reasonalbly priced.
For SQ focus the cost of speakers on the front. Conventional wisdom will be that seperates will do far better for SQ. Folks here will have preferences on brands, but let your own ears do the shopping, please don't buy speakers unheard! You will live with them day in and day out, so find some you really like the sound of. The stock size, 5x7/6x8 are easier to install, but not as great a variety. There is a good deal of discussion regarding there merits or vices, but for SQ they can do just fine. 6.5 are more of a challange to install without some creativity, and there are lots more choices. The question is how much lower the mid bass will go in a 6.5 vs. a 5x7, do your own research, the answer is actually it is a toss with most brands. For SQ- you want a clear soundstage across the front, from a distinct left to a distinct right, with a clear soundstage having a center.
That actually means rear fill is not required if the speakers and the install and the tuning of the system holds that front stage together correctly. I have not seen many serious SQ competitiors ever use rear speakers, and in my SQ car I do not use rear fill. The rear deck holes can be used to vent the sub to the interior. If you are going for rear fill, get a amp that will allow you to crossover and kill all highs to the rear at the very least. I would look for sonic matches to the front, and then only in the mid frequencies.
For SQ you won't need a killer sub, and frankly that is one area I don't focus too much energy. Low bass is not a virtue or required for SQ. You do get benefit from high efficency ratings, and low distortion rates. Subs normally have distortion rates up to 25% at rated frequency and power, so try to get that number as low as you can. You will not want the distortion or a loud thump, you are seeking a sharp kettle drum.
Amps are a interesting unit in a pure front/sub set up. You may not need two amp. Get a good clean bridgeable amp instead, run the front channels and the the bridge to the sub. I have seen many nice clean SQ setups run this way. Once again, becuase you are not looking for overpowering bass in SQ, the bridged output will do a decent job in powering a sub. Once again, distortion, channel seperation, and slew rate are the big numbers in SQ amps besides frequency response. You want at least 20-20,000 feaquency, a distortion rate of .001 or lower for rated output, a slew rate greater than 100, and seperaton of at least 90Db.
I will be most interested to see what you finally choose, good luck and keep posting!!

 

Thanks for the insight Dave. It would be nice to audition speakers but i've checked at all the local places and all they carry is the typical stuff: rf, pioneer, kicker, etc. Is there any brand subs that your recommend for what i'm looking for? Also would a single 10 be sufficient for my needs? I like the idea of using a single amp and just bridging it.

Things that are confirmed:
Alpine 9813 HU: 299
DEI studio 6.5 components: 118

 

just as long as your run atleast 300 watts rms or so

 

see wright01, am am not even sure that it has to be that much if done right!
It would be a function of the ratio of the fronts to the rear. Remember, this discussion is about a SQ system. Catatgories go as low at total wattage of 100watts in competition!
Granted you are correct for overall sound in a moving car with road noise.
For SQ you don't want bass to be overwhelming at all.
Beernut- a 10 inch is fine, even considered by some the preferred sub of SQ.
JBL makes a decent sub for the dollar, at a higher cost Boston Acoutics is nice. I will look around and see if I can find the card of a guy in San Diego who sells factory seconds on Eclipse subs, nice and good looks to boot!
Many of the folks here will tell you brands, just remeber to look at the efficiency, the frequency response range, and the distortion ratings of the specifications.
I also like the infinity powered basslink, but that might add to the budget. It comes stock with an adaquate amp, and a volume control. Down side is it gets you back into two amps again as a set up.

 

i got those numbers coming from a infinity reference setup with 1 set of componets, one set of 6X9's and a 10 referene woofer in a .65 cu box with 280 watts. if you run only 150 watts, you won't hear the sub. also the speakers are ran from the HU.

 

beernuts, i guess crutchfield has a typo then

 

Hey Beernut, where do you get the 9815 so cheap?

 

www.ikesound.com