The "Zone B" outputs are supposed to send the audio to another room, in stereo format. That means one can use the particular AVR as a DAC with massive power reserves! That is if one forgoes the center channel, and you probably must because otherwise the content for the center channel will be at +3db boost. Probably weird.
As I think about it, the idea is to get towers for front speakers and a center channel so that the dialogue is clear at all times. They say that operating without a sub (and assuming an AVR) "puts a real strain on the amps and robs the midrange drivers and tweeters of the power they need to create an expansive soundstage with massive dynamic impact".
As stereo amps don't suffer from that after a certain price limit (assuming class A/B operation), the Cambridge Audio CXA80 has a shot I think. They are not supposed to be combined with a sub, after all.