If your after just a sound upgrade, forget amps. Amps are usually used for pumping and thumping and sub woofers. You can get a decent head unit and decent speakers and it will do you nicely. It all depends on what kind of music you listen to as well. But for all round, i would go a Kenwood, or a JVC headunit. With Kenwood or Pioneer 3 or 4 way speakers. If you want more info msg me personally.
**Working PART-TIME for Carjunky for a while, Please bare with me =)**