1. I just recently bought Polk Audio R50 and are wondering whether it is necessary for me to buy either Polk Audio CSI20 or CSI30 to use as my center channel (which one would better fit?). Can I use Infinity Entra 2 center channel instead (Would it be better than use center channel of Polk Audio?) 2. Between Polk Audio R50 and Infinity Entra three floor standing, which one is considered a better grade? Thank you so much for your generous help?