csi a6 center
Fxi A6 surround
I really need a subwoofer bad I know there are better ones for the same price but I really want a polk sub . Is the pro dsw 660wi a good subwoofer .
I have a similar system as you except I'm running the RTI-A7s as my fronts and I have RTI-A3s as wide channels. My center is the CSI-A6 and I have the FXI-A4s as my surrounds so I get it, you like Polk. But I would not recommend doing the Polk subwoofer. Polk's not necessarily known for their subwoofers. But perhaps that's just my humble opinion. What I do know is I've had them in the past and they just don't compare to the ID companies. Getting the PSA XV15 was one of the best purchases I've made for my HT.
At $220 I would look at the BIC F12, Amazon has it for $182 right now. I've heard a lot of people recommend this as a good sub in the $200 range. Personally I would save up and do what Kini suggested and look at the SVS PB-1000. It's worth it.