I think those are actually multi-zone connectors. You wouldn't run both at the same time. They're in case you want a different speaker config for different types of sources. For instance, you could place two speakers identical to your fronts on the 2 zone two channels and dipoles on your regular surrounds. If you put in a video DVD, you could then have the traditional 5.1 setup and you could switch to having four identical speakers at each corner while listening to DVD-A, which is how DVD-A is mixed.
You may be able to put two speakers on those two connectors and split the power (not sure how the non-7.1 receivers from Denon handle this) but there wouldn't be much point.
