I have almost your exact system; a 7.1.4 using an ATI6005 for my fronts and sides, and an AT527 class D for my rears and atmos. I also have three dedicated 20 amp lines. I have never had any hum issues. In a previous system I had a hum that I traced to a cable box.
ATI AT6007 amplifier hum
Long time reader and first time poster. I recently traded in my Pass Labs X600.8 amps to ATI AT6007 and AT528NC combo for my 9.1.4 setup. I have 3 dedicated 20A lines which I’ve used previously for the pass labs and now for the ATIs. I did not hear a hum from the pass labs but I’m now hearing a hum from the AT6007. I’m also using proper 20A power cables. There is no hum from the AT528NC. Please advise. Will I need a DC blocker or power conditioner?