Every time I make a change. Sometime during my mis-spent youth I suffered brain damage that affected my short term memory (you know like forgetting where you put your car keys). So every time I switch one cable for another or one component for another, by the time I get back to my couch I can't remember what it is I'm listening to.
Actually, I don't know anyone in my real life who would have any interest in doing the switching for me, nor am I sure I would be interested. I am perfectly happy deciding for myself that the new amp I bought sounds better than the old one. I trust myself to do this, because, for example, I have brought amps home to audition and determined on a sighted basis that if there was any difference, I couldnt tell or it was so subtle that I did not need to make the purchase. I have no interest in impressing anyone or any part of my ego invested in my hi fi equipment (I didn't design the stuff).
What I have said recently, and have heard privately from some real pros, some well known, is that properly designed inexpensive late model amps and cd players get the job done as well as expensive stuff, and no one has published a report of a rigorous blind test that shows otherwise. I wasnt really happy when one of my favorite reviewers told me that there isnt much of a difference between my expensive cd player (I paid a little more than 1/2 the retail) and a NAD. I dont even agree with him. But I wouldnt want to put any money on my belief.
The other thread to which you refer is hilarious. The author turns everything on its head. Scientists and professional engineers use double blind testing all the time, but he calls DBX "pseudo-science." The camps are usually divided into scientific objectivists (those who argue for DBX tests and say all cables and properly functioning amps sound the same) and subjective relativists (audiophiles who believe that everything sounds different), but the author of that thread calls people championing an objective scientific approach "subjective relativists." There is no way to begin to have an intelligent conversation on the subject
I am not one of them, but I respect the scientists and engineers I know who advocate DBX testing of audio components. I dont see how you could find fault with them. They're trying to save you money and redirect your attention to things that really matter - speakers and room interaction.