Hey, thanks for the info I'll start looking around at some of the products you listed, I guess my only question now is, lets say I replace the speakers all around with the Focal Polyglas line, pick up two JL W1's (10") and get that put in with the factory deck, how is it going to sound. Will it be clear with a nice bass hit, or will the fact that I cant control sub bass and speaker bass differently ultimately end up killing the sound no matter what I put in it. FricFrac mentioned just adjusting the gain to get the desired level of base, will that actually give the level of clarity you would want?

-polarity

Using the stock head will yield suprizingly good results. In my 2005 350Z before i sold it it Ip put all the factory stereo equip back in but left the speakers and i was amazed at how good it sounded. It wasnt far off from the what it was fully amplified. Do a speaker level conversion from the stock sub output to a subwooferamp with remote control level and that way you can better balance the bass between the subs and the mains independantly.

Remember, Amplifier gain is not a volume control. It is meant to match up with voltage output of the head unit. Also it is not necessary to replace the rear speakers. Leave them stock, you wont notice the difference and it will save you cash.

Another brand of equiment that s really good stuf for the money is Alpine. Their amps may not be the most powerfull for the money but they are very reliable and they sound pretty good for the money. I have paid a premium for top-end JL Amps and they have awesome power and sound but I was blowing them left and right. Avoid thier 5-channel amp at all costs!

So, I can hook my 4-channel amp to power the front and rear speakers without replacing the factory head unit? Or should I just replace the speakers and ditch the amp, i mean i already have all the gear from a previous install, so i minus well use it right?

Yes you can. You will need a 4-channel line level converter such as this device.

Scosche SLC4 Four-channel line output converter at Crutchfield.com

You just wire the speaker outputs from the stock stereo into this device and it will convert signal to line level and you can use rca patch cables to your amp.

I would ditch the rear speakers and power channels 1-2 to your fronts. Install some good component speakers. Then the bridge the rear remaining channels for a subwoofer.

You could have a nice system for a few hundred bucks.