Laura, as Ken indicated, the reply you got from Denon was incorrect on the surround B option. Ken described it correctly.

You only have seven separate channels available and if you use the back surround channels for back surround speakers you can't use them for zone 2 speakers at the same time. Also, wiring the back surround speakers to the surround B terminals doesn't work right since the surround B output is side surround material, not back surround.

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Enjoy the music, not the equipment.