Amps are a tricky thing to shop for if you are unfamiliar with them, because they sell cheap ones that described very similarly to the decent name-brand ones, but are horrible quality. I've only ever bought one amp (a Rockford Fosgate which I'm very happy with), so I'm not really qualified to give advice, but hopefully someone here with a little more knowlege can give you some basic advice.

I will venture this though...you might try Crutchfield, as their sales people seem to be knowlegeable and they don't even stock the cheaper crappier amps.

The lineout Converter for your existing head unit that I mentioned above can be found here (pic) or you can get one from Crutchfield or any decent local car stereo installer.