Correct.
It's a little difficult for people to get their head around that two could be better than four, but think about this for a second:
Everything you are listening to in your car has been formatted for a two channel (stereo) sound system. There is no additional audio information being presented in the rear speakers. The rears just duplicate what the fronts are playing.
What this means, is you have the same sound coming from two different locations within your vehicle. This confuses your brain, as it doesn't know where the sound is coming from. People like to think that it allows the sound to "surround" them.
With a good set of front speakers, properly set up, you will create a much cleaner soundstage, and make it a lot easier for your brain to locate objects in space. A properly set of fronts WILL surround you with sound, and will sound better than any standard 4 channel setup.
My advise, make a set of brackets to fit a 6.5" woofer up front (it's easy, just search on here), and get a good set of components. Run them off their own amp so that they have lots of clean power available, and it'll sound damn good.
As for head unit, the more tuning options the better you can make a sub-par installation (or equipment choice) sound. I would suggest a Pioneer DEH-P880PRS. They can be had refurbished on ebay for a few hundred.