I would power the rear speakers with the amp, since they're further away from the driver and they're 6x9's and should compliment the amp pretty well.
As for brands, I like Infinity, as I have their component set in my truck. I've never heard anybody complain about the way an Infinity sounds, and you should be able to get a pair for what your g/f is looking to spend.
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the ZEB. They have the cheapest prices I've ever seen. I've bought from them on 2 seperate occasions, one being the bulk of my stereo equipment I have now. I spend around $400 there when it would have cost me over $800 anywhere else. They don't have Infinity, but they do have a lot of other good stuff. I'd also look at Directed Audio. I've had good experiences with their 6x9's, since I used to have them in my truck before I bought the Infinity components.