Not true.  An atheist does not believe in the things you mention. You cannot confidently rule out such things in any absolute sense.

I am a Christian believer and it would be just as easy for me to say that I rule them in (which I don't). I just do not believe that God is interested in making a hifi system sound better!  Or that any voodoo etc is concerned in making hifi sound different.

IF the effect is consistent and repeatable, then there must be a rational explanation.  The fact that the explanation is unknown to us at the moment does not make it non-existent.