dvzzz -- you don't need a line conditioner for the 7100 to work correctly, but it should quiet the transformer hum (unless your unit is defective). The Outlaw might be humming when the others don't because of its toroidal transformer design. My Sony ES receiver never buzzed, either.
I just received my $189 A/C conditioner this morning, so I'll know by tomorrow if it does the trick and will post on 5/21 with results.