Perhaps I missed it, but I don't see anyone considering that vibration in the cables/cords are as big or bigger a factor in degraded sound performance as electrical interference. I keep my power cables as far as reasonably possible from my ICs and speaker cables because I can. My experience over the years is that it does make an audible difference with certain brands and models of cables. I don't find it makes much difference with my current cables, but that's part of the reason I chose them. Isolation from vibration is a different story. The power cords seem least affected, the speaker cables definitely benefit from vibration isolation, and the ICs are the most sensitive. When something sounds "off" nowadays, I invariably find one of my cable separators has gotten knocked loose allowing an IC to contact a wall or some other source of vibration. It's an easy and immediate fix. I'm meticulous about keeping isolation factors from affecting my components and it pays off. It's much simpler and far less expensive to keep the cables from picking up vibration via careful routing and relatively inexpensive cable isolators/separators.
I have been a stickler about keeping power cables away from signal cables...on equipment ?
What I am finding very interesting, and to some extent, disturbing, is how close the power IEC inlet or power cable, is designed so close to the speaker or input / output terminals of amplifiers / gear. Many of my Hafler, Bryston and Citation amplifiers had / have this arrangement, and many of these newer and smaller chassis class d amplifiers have this arrangement. I have actually rewired ( or had rewired by a tech ) a different path separating the power line to the audio line within the chassis, and hearing a cleaner background when listening to music through these products afterwards. I am finding this to be the case, looking at photos of some other gear as well. I also believe, power switches and it's wiring, should be designed at the rear of a component, for the reduction of ac related noise, even though it might be an inconvenience with it's daily operation. Just as an aside.....I keep my gear on 24 / 7, unless I am on an out of town trip. Your thought ? Enjoy, be well and stay safe. Always, MrD.