I had been listening to my system long enough that I knew how certain discs sounded, and as a result could pick out the improvement. Is it subtle? Absolutely….you have to know the disc that you are listening to and how it sounds on that system intimately in order to be able to hear a difference when it comes to the soundstage and the clarity.
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.
With regards to your comment on being a sound engineer and you couldn’t hear a difference…there are more than a few experts in the field who can…
From stereophile on PS Audio units:
“Listening to the system with AC coming directly from the wall socket rather than the P300, I was struck by how comparatively lifeless and flat the music sounded. It was almost as if someone had turned down the volume while I wasn't looking”
http://stereophile.com/powerlineaccessories/460/From Soundstage on Audio Magic units:
“With the Audio Magic Stealth, "bass had new authority" -- " a meaty vividness and three-dimensionality about it that was amazing"; there was "also now a sense of expansive space that was completely new"
http://www.soundstage.com/revequip/audiomagic_stealth.htmBut hey, if you don’t hear the difference, then don’t spend the money…given the fact you’re a sound engineer I am sure that your opinion based on no practical experience is more sound than mine (and others quoted above) who actually have given their ears a chance to make the distinction.