B&K Sonata M200 + Polk Rti A9’s

i have the m200s ($450 is an excellent price btw) and they will be more than enough for your polks and a whole different level than your avr.

thanks  for your reply LoomisJohnson. 
  What kind of difference can I expect to hear,  Will it really be that much? I know my receiver is just a receiver but as I understand it’s a pretty beefy one , no?

i would expect a night-and-day difference, both because you m200s are more powerful and because they're  higher-quality amps than those in your avr, which have compromised power supplies, less robust transformers, etc. typically i'd expect more low end control and overall detail.

I have a pair of them (+ a single one I use as a center channel). I have had as many as 6 at one time. They are great sounding amps even ignoring the power and current output. I use them to drive Totem Mani 2's which themselves are very power hungry.

At that price you should grab them (assuming they are in good operating condition). Many of them out there are a little dinged up, and some of the older ones are pretty utilitarian looking, but they still sound great and are bullet proof.