11-06-11: Dan_edHi Dan,
I think I get it, but see what you guys think about this. My two amps hum because they reference ground at a slightly different potential, and that creates a small current between them when they are on the same circuit. The balanced connections assure that all components plugged into it reference the same ground so there would be no potential between the amps.
See the second paragraph of page 2 of this Jensen paper. A key factor in how much hum reduction would result is the stray capacitance within each component between each of the two ac input lines and chassis, particularly stray capacitance in the power transformers of the components, and how similar or dissimilar those stray capacitances happen to be. So while I would expect there to be SOME improvement, the amount of improvement figures to not have a great deal of predictability.