A:Answer Hi Jeff,
The AVR-S760H is designed to handle one pair of speakers with it's Zone 2 feed. If you wish to experiment with running 2 pairs of speakers from your Zone 2 feed, it would be wise to use a speaker switching box (such as a Niles SS4).
It is recommended to play either the Main Zone or Zone 2, but playing both zones simultaneously may not work out so well depending on how demanding your speakers are and how loud your playback volume. In particular if you have two pairs of speakers driven by the Zone 2 output - even with a speaker switching box.
Unfortunately, the impedance value only tells part of the story. There are a few other factors to consider before it is possible to be more conclusive about what can be handled by any given receiver when it comes to speaker demands.