John, the best way to protect the electronics, frankly, is to pull the plug out of the wall. A surge suppressor may be of some help for the relatively rare surge strong enough that AV equipment doesn't handle it routinely(which AV equipment is designed to do), but not so strong that everything goes up in smoke. The Tripp-Lite units such as
this one do that for a reasonable price.
As to "line conditioning", that's what the transformer, rectifier and filter capacitors in the power supply section of receivers/amplifiers already do. Clean DC is supplied to the amplifying section and no external unit is necessary to do this.
