4 10's will give you 314 ci of suface while 2 12's will give you 226 ci.

So what does that mean? 4 10's will be louder than 2 12s if they are the same in make and power ratings.

The thing you have to think about is...12s hit lower than 10s because they have more surface area...they can move more air per oscilasion.

What you need to do is replace the deck. Because you do have shaker system you also need new speakers.

Get two 4 CH amps. One amp will power 4 speakers and the other amp will push the other 2 speakers and subs.

2500s will get you a great sounding system but also can get you a system that sounds like crap if you don't know what to get. Do some shopping and listening.

Be patient. And dont be affraid to work in steps. Buy the deck and speakers now and the amp and subs later.

Or if you want to do all at the same time then go for it.

A word of the wise though....unless you give your speakers more than 35watts RMS each then they wont sound louder than your shaker.

 

You should only need 2 speakers. Get a good enough frontstage and you wont even notice there are no rears.

 

First off I would definatly replace the Stock unit with Clarion or Alpine. Get a decent componant set maybe the Infinity Perfect 5.1. For your mids also would go with Infinity. Now for your bass I would look at JL Audio 12's with a Rocford amp. You will also need an amp to power your componants or you could go with the single speakers for the high's and let the head unit power the highs and mids, while your amp is striclty for the subs.

I built my system under a much less budget. I have an old Kenwood unit I have had for years now with eclipse 3 1/2 in the dash nothing in the door 5x7 pioneer in back and 2 JL 12's with Rockford M150 amp. I got all this for about $800.

 

Im thinking of selling my audio equipment from a previous car I no longer own, Maybe your interested? I wont have the model numbers till sunday though. Everything is in storage.

4 Alpine 12" Type-R DVC's, 2 of the subs are still unopened.
Alpine Head Unit-CD Has "Bass Engine, can control sub amps, full crossover etc.."
1 4 Channel Alpine V12 Expert Amp
1 2 Channel Alpine V12 Expert Amp (1000 Watt)
1 2 Channel Alpine V12 Expert Amp - This amp is unopened.
1 Set Boston Acoustics 3 Ways - I think there 5.5 or 6 inch. Cant remember
1 Set Boston Acoustics Door speakers, they were components but I forgot to get the crossovers out of the doors before I treded car in - 5.25 I think
Plus a bunch of other stuff thats just laying around that I just never even opened.

Everything is in brand new condition. PM me for more info.