I purchased a pair of M700’s this weekend with a Demo P5. I have a Rel R328 that I’ve used in my past systems that I absolutely love. I was hesitant to plugging everything in and worrying about the possibility of humming coming from the subwoofer. Unfortunately I have some problems with the P5, so I hooked everything with a standard power strip. One wire from the sub goes to each positive terminal of the amplifiers and the black ground wire, do nothing with it. Walla, no hum, buzz or feedback. Perfect, with power on or off, dead silent for me.
I leave everything on 24/7 including amps, sub and DAC (DirectStream). I hope this helps others who were wondering about the connection issues.