Need Speaker Advise

[dukerock12]

I see that on newegg the monitor 50s and cs1 are on sale. Ive been wanting to purchase polks for a while now and may jump on the sale prices. My question is which polk speakers should i get? my room in about 11x13; i sit about 7-8 feet from the front speakers. ive been wanting the monitor 60's with the cs2 and some monitor 40 surrounds but with how small my room is will i notice the difference by going with the 50's and cs1? im on a budget of about 500-600 dollars. if i get the deals today it would leave me with some extra money to spend on a good subwoofer. is it possible if i buy too good of a subwoofer for the monitor 50s it will over power my speakers? And one more question...If you look at my home theater pictures, the speakers i currently have now, ( Onkyo HTP-750x) are the polks much of an upgrade for the small room or should i just stick with the speakers i have now?

sorry for being such a newb, thanks for any help