It does not have 9 channels of built in amplification, it only has 7. You will not be able to run a 9.1 setup and also a set of zone 2 speakers with all of them running at the same time, unless you also add some external amps. The A+B power spec only means, that the two pairs of speakers when run as A+B at the same time, would also end up sharing the same power output. Start looking more at page 84 of the manual under "amp assign". Do not go by just by what you see on page 10, where it mainly only shows speaker connections.
BTW, Denon's calling it 9.1 is kind of bogus, when all it is really doing is doubling up on the L&R surrounds (A+B) that are also just sharing a common power output.