Found this on Audioholics in an ariticle on amplifier claimes. Their math looks correct to me.

"How can my amp claim 200wpc / 400wpc x 7 into 8/4 ohms, respectively, ACD?

Any amp can claim anything… but as for actual delivery - it can’t. Unless, that is, it has two individual and independent power cords feeding multiple power supplies. In order to achieve 200wpc x 7 continuously with all channels driven, it would require a whopping 3111 watts, or two 120V dedicated lines consuming almost 13 amps each!

An amplifier claiming 400wpc x 7 into 4 ohms, all channels driven, would require over 6200 watts! That’s 3 ½ dedicated 15A lines running at full power — or, perhaps, a mini self contained nuclear reactor in your home! Remember Three Mile Island? Those guys liked their music LOUD!"

From what I can tell the 7700/7500's don't have multiple power supplies.

Read the whole article. The All Channels Driven (ACD) Amplifier Test