Last time I checked, we hadn't gotten a manual yet, so we don't know how it handles balanced/unbalanced selection.

A 7x200W amp plugged into a 20A circuit is not likely to ever be able to output a full 2100W of power to its speakers simply because of the circuit's limitations. A breaker will actually trip before delivering its full rated current (if I remember the EE's at work correctly, it's around 75% to 80% by design) - for a 20A breaker, that means you will get 15A or 16A at most. That equates to 1800W or 1900W of input power. Class AB amps are not exceptionally efficient, which is part of the reason for all that weight - they need to reject the waste heat, which is most effectively (and quietly) done with big heat sinks. With 1800W of input, you're probably not going to get more than 1000W out (although I'm just guessing there, as there's almost no hard evidence available available). This will also hold true for the 7900. With two 20A circuits, there will be close to 30A of total power available to the two power supplies, or roughly 3600W of input power. With a single 20A circuit shared by both power supplies, the maximum input current falls to around 15A or so before the breaker trips. What that means is that a couple channels could still do a full 300W of output, but only if the other channels weren't being placed under too great a demand.

Oh, and yeah, it's 9.5 inches tall (not 95). You'll want to check on space and on supports, because in addition to being huge it's also mighty heavy.