The simpler test is to plug the system into the wall and turn the volume up…I heard faint static, or noise in the background. Upon hooking up the Audio Magic or the Monster unit, the noise went away….complete silence by my ears…a black background as it is commonly referred to as.
Most peoples stereo's exhibit this until they introduce some level of "clean power" be it a dedicated circuit, a power conditioner or a regenerator...
I had some nasty and fairly loud background noise before I moved my playback to the other side of the room and switched outlets. What's different between the two? Dunno. But I do know the noise is dramatically reduced. Could a power conditioner on the other outlet have achieved the same impact? Dunno. But it doesn't seem unreasonable that it might.
I dont think anyone here would argue that clean power is not important. It is.. but what are the benefits to the "soundstage" ?
For example, others have mentioned "blackening" of the background. The audible end result of this blackening may appear as an improvement in soundstage because low level detail is no longer masked by noise.
and can this clean power difference be heard in audio equipment that already filters out most of the line noise in the first place?
You're assuming the audio equipment effectively filters most of the line noise in the first place. As with all playback / recording gear - and you know this better than many here - designers and manufacturers cut corners in order to achieve a specific price point and target audience. The cleaner the power, the less filtering is required by the playback gear. Seems reasonable that the more filtering performed by a better filter, and the less performed by a mediocre filter, the better the overall filtering.
I say great, if that's so make a recording of the before and after via a cd player and a digital recording device so we can all hear that difference and lets do some A/B tests.
Respectfully, I think the best way for you to do the A/B test is to go buy one - or several of varying quality / feature sets - and see for yourself.