Smitty, your QS8s, even when mounted on the back wall, are still side surrounds in a 5.1 setup. They should therefore be separated as widely as possible, even by varying distances, which can be compensated for by correct level calibration.
As has been discussed, actual biamping can't be accomplished with a Denon or any other receivers which have such a "feature", so yes, it's essentially meaningless marketing. There's only one main power supply section in a receiver and the output transistors in the several channels operate as valves to meter that limited supply out to the connected speakers as needed. The transistors have no power of their own and simply funneling the power to a speaker with two sets of output transistors(one previously unused for back surrounds)instead of one can't double the power, as some imagine, or increase it by any amount.
