What levels do you listen at? The power hunger comes from cranking the volume up. You could be a candidate for adding a power amp, it's fairly simple to integrate the ampd with the channels the avr is powering, in whatever mode you use the avr in. Keep in mind it takes a doubling of amp power to gain 3dB spl. You might play around with
this spl calculator to get an idea of the relationship of your speakers' sensitivity/your distance/amp power. The Polks I believe might dip to a fairly low impedance and may have some tough phase angles which might also be an argument in favor of more substantial amplification depending on your levels; you might want to look up measurements for your speakers. IMO you're more likely to damage your ears than the speakers by listening at high levels, tho.
A good sub is a good thing, what do you have particularly?