Digital amps can be very effective, but they are new technology that is still maturing. The benefit is appealing: less waste heat, which also means less power consumption (perhaps not enough to see on the utility bill, but still helpful), fewer heat sinks (less material cost and less space needed for the amp), and a smaller power supply (less copper to have to buy). To say that traditional amps are "bad" because they produce almost as much heat as they produce power for sound (it's not necessarily a one-for-one relationship unless you're talking about class A) seems dubious to me.

Your friend was correct about the 990 and 7700's balanced designs. The 990 is not balanced all the way through, from what I've heard (there are few surround processors that are). The 7500 and 7700, on the other hand, are fully balanced.

Having never heard the Bel Canto, I can't speak to how it compares to the 990 for music, but the 990/7700 would be a sure-fire step up from the ol' 2105.