I was looking to upgrade my Infinity Alpha 50's with Paradigm Studio 100's. I was so excited to hear the Digms. Once I did, I was a little disappointed. They were better than my speakers, but not much better, and not better enough to justify the enormous cost difference.
You are also looking at the step down Paradigm line. I would venture to guess that the Polk RTiA9's will be every bit as good. Listen to both, judge yourself. If the Polk's can come close or beat the Paradigms, and your saving money....that is gravy. I'm actually interested in hearing the Polk A9's, and see how they compare to my current Infinity's. Anyway, good luck with whatever you decide.