I mostly agree with norton: audiophiles are sitting ducks when it comes to taking advantage of the placebo effect. Furthermore, science can explain a lot about acoustics, and even psychoacoustics; if a given tweak has no plausible scientific explanation for its effectiveness, I approach it with skepticism. BUT...it is also the case that not everything experienceable is measurable. People were enjoying savory flavors for centuries before neuroanatomists found the receptors for what is now called umami. The phenomenon existed, and was experienced, before it was scientifically understood.
That said, I remain skeptical about most claims for power cords and cables (especially "break-in" and directionality), and I don’t hear a difference either. And the Schumann resonance generator is not even a do-nothing box.
But sorbothane under the feet of my Scientific Fidelity Teslas did improve the clarity of the bass and the general cohesion of the soundstage. Not dramatically, but noticably.
By the way, I also own a pair of PSB Synchrony Ones. Because I like the sound of the Teslas better, I canibalized the feet for the PSBs, screwed them into the Tesla’s base, and THEN set the speakers on sorbothane disks. I won’t go back.
For what it’s worth, though, room acoustics—as pretty much everyone knowledgable here will agree—have a far greater effect on SQ than probably any tweak. But it’s a moot point. We have the rooms we have; few of us are in a position to build a room specifically with our music, and our music system’s requirements, in mind. Hence, the passion for squeezing just that little bit more out of what we’ve got.