Nunya, Polks being a bit on the bright side do best with a warm, full bodied receiver and in your price range I would suggest the NAD you mentioned and my favorite in this range, the Marantz 5400. The Yamaha 750 and Denon 2805 are too thin sounding for Polk and work better with Paradigm or PSB. In the Yamaha line I would not recommend anything under the 1400, which can be had for under $600 mail order but the NAD and Marantz are much better match's with Polk. Check out the Marantz 5400. Hard to beat.
therealelitefan, Thanks for the feedback... I can also buy Marantz @ the place I'm considering the Polks. I will do as you suggest. Speaking of the Paradigm's.. I went today to listen to the Studio 40's - A full complement of Paradigm's(studio 40's/cc470/ADP470's) would cost double the Polks! Are they worth it?
Nunya, Only you can answer that question. The real question maybe is the Studio series worth double the Paradigm Monitor series? Listen to the Monitor 5 and 7. As I see it for your original budget you can go two ways. First is the Marantz 5400 and the Polks or the Yamaha 1400 and a Paradigm Monitor system. Both are very nice. Only your ears can tell you which way to go.
I'm still looking for a new receiver in this range and I haven't yet decided between the T743, SR5400 (or new SR5500), new Onkyo SR602 and Pioneer 52TX/53TX. They all have their strengths and weaknesses, but I think these are the best options in this range for most speakers.