You're almost right with regard to balanced and unbalanced signals, except that unbalanced signals often also have a shield that's not part of the signal circuit - look at the Outlaw audio interconnects for a great example.

But the OP seems to be asking about balanced vs unbalanced ampifier output stage designs. I don't feel comfortable enough with that subject to try and explain it to someone else.

EDIT:

I think the 7700 is a balanced output (and input) design, the older amps were not.