If you're on a tight budget I think the polks are the better way to go, and a high end head unit isn't really a necessity, seeing as the speakers will be getting their juice from an amp.
Not knowing your current stereo set-up however, you wanna keep in mind you aren't going to get a lot of bass out 6.5" speakers, and any sort of subwoofer would really add a lot to the whole package, even if you had to get some cheap Walmart type amp to run the subwoofer in the mean time. Just my two cents. http://community.crutchfield.com/forums/
^^ There's another great and quick source for stereo advice and guides on correctly wiring your speakers to your amp.