The A and B setup on the Denon 3805 is when you have four rear speakers. One set would be for movies (maybe an extra pair of QS8's) and one pair for music (maybe a pair of M22ti's). See page 22 of the owners manual.

If you choose to use Zone 2 without a preamp, my understanding is it uses the rear channel to Zone 2 and you then would only have 5.1.