In my case, there are no other electronic devices near my HT equipment. Bringing down the noise level in its immediate area is being handled by my PS Audio Ulitimate Outlet, an APC H15 Power Conditioner, and a Mondail Magic Coax Ground Isolation Device.
The final step is the shielded 2-wire IEC power cord connections to the equipment itself.
I can't/won't mess with the 3-prong devices, and will not modify the equipment that does not have detachable power cords.

If concerned about AC line interference (EMI), there is a very effective and technologically solid way to combat it. That is using balanced power to your equipment. This is what major recording, film and broadcasting studios use with their gear.

Essentially, what this entails is a center tapped isolation transformer which plugs into the "unbalanced" AC line from your wall. The center tap on the secondary is grounded, and the outer legs of the transformer feed your equipment balanced 60VAC phases, which add up to the standard 120VAC. This scheme acts exactly like balanced XLR interconnects in that any crud on the AC line cannot get through due to common mode cancellation.

That way, your AC cables have NO external field, zip, nada. This method is far more effective than shielded power cables, and will reduce noise inducted through the AC mains to nothing.

Equitech makes a line of balanced power transformers which are used heavily in the professional industry.

Equitech Balanced Line Transformers