You can use the p363s just fine with the Onkyo, so don't worry about impedance. The worst that could happen is if you blast them for a long time at a loud volume, the receiver will just shut itself down to cool off. Even that probably wouldn't happen. I have run the p362s on a variety of different receivers and amps, never had any problems. The idea that lower impedance speakers can not be used with lower end receivers is kind of half BS. As for the Polks, I have listened to the Rti8s, liked the bass, didn't like the treble. I would still go with the Primus, especially if you are using a subwoofer. I haven't heard the Bic venturi, but looking at that design, I definitely would not trade the Primus speakers for them. As for 5 primus p163 speakers, that approach has its advantages, but I would go for the the p363s and a c351 center (better yet use a p363 as a center if you can). The p363s will be more powerful and have a sharper mid range thanks for Infinity's terrific CMMD mid woofer.