We insalled that Marantz and connected it to a Krell Showacase 5 channel amp via XLR and had nasty hum as you described. We also had the same hum, but a bit lower in volume from the LCR which were active M&K speakers, connected to the Marantz with unbalanced interconnects. We could not fix it completely. Marantz tech. support told us to use a Marantz amp because they had not had any noise in their experience with both products. Brilliant, eh? Reviews across the interwebs complained of humming and buzzing with the Marantz 7701, so we returned it and put in an Anthem AVM50v and no hum. And surprisingly, no HDMI issues. :P