Not sure what you mean more power out of the B&W speakers, would take a doubling of amp power just to get 3dB more spl out of them and they're only rated for 100w as well. Subs would be a good idea for those B&W speakers, they don't go very low and I'd want to use bass management rather than only get LFE channel thru the subs, too. The avr you have now has sufficient power I'd think to get pretty much all you're going to get from those B&W speakers and the other avr you mention has close to the same amp rating in any case. Modern avrs aren't useful for passive subs as they'll only provide a sub pre-out. Don't put too much importance on a wattage rating of a speaker, impedance and sensitivity are more useful.