If this is just A/V equipment the biggest factor is to just be sure everything is plugged in the same place so all of the equipment is using the same power and ground. Then bond the frames of all equipment together. High end equipment usually has a bonding lug to do this with. Then you won't have that nagging 60hz ground shift and hum.
You start having troubles when you have a couple power sources and cables strung around the house.
Electure has a good point about the IG receptacle. In a plastic box, just use a regular one
