At $1300 it would be hard to beat the 7701. It is also more future proof since it can not only pass 3D but also the possible 4K video in the future. I would definitely take the 7701 since the price is about the same.

As far as your 7700 hum have you considered taking the top off and trying to find a loose part inside the cabinet. The 7700 has seven channels in the same size box as the 7500 so there is less room inside. Maybe a cooling fin or loose chassis screw is causing your hum. Have you tried disconnecting the channels one at a time from both input and output to see if it is related to a single channel.
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Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner