I have a background in experimental psychology and as you are aware all attempts at measuring things have inherent error that can never be completely eliminated. You are essentially setting a bar that can't be attained if you are asking for infallible testing. And randomized assignment is no guarantee that groups will be equivalent, there still exists the chance that during random assignment the groups will become biased simply by chance. And yes, while there are differences for certain in the fact that an experimental situation can differ from a natural situation, you can't simply assume that the possible differences are significant enough to invalidate any findings. That is why we have statistical analysis that control for measurement error. Ultimately the more sets of data that converge around a question, the greater the sample of the population becomes and the greater confidence we can have in the results. Is it perfect? No, nothing ever is, but to suggest that because some measurement error exists that the results are unreliable is a gross over-simplification.
When it comes to memory issues and subjective bias, the body of scientific evidence is enormous and if people like to hear it or not, audio memory is not very robust at all. If you think that our brain can listen to a song on a particular system, memorize the tiny sonic nuances that differentiate it from another similar, but not identical system, hold those impressions in a robust, easy to access memory location, retrieve it hours, days, months later and allow us to compare very minute differences with any degree of accuracy I'm not sure what to say. I believe in the subjective joy of this wonderful hobby, it is crucial and important to me, but for people to disregard science simply because it doesn't confirm what they want confirmed is difficult to reconcile. How about taste, that is another subjectively experienced sense in some respects. Do you think that our brain can remember with incredible precision taste experiences from the past? Could you reliably pick out the differences between two garlic samples of the same species, but grown in different locations? Not likely, so why is our hearing brain supposed to be capable of these extraordinary feats of memory magic? Why on earth would evolution give us such a capacity, how would it help the species survive? Our hearing brain is remarkable, but it is also extremely limited in many ways and people just need to accept that.
Many of the claims made here at head-fi are simply assumptions people make because they have heard others tell them that they can do it so transitively people just take it for granted that they have these abilities and there is nothing you can do to convince them otherwise. Rather than ask for perfect scientific evidence it might be fruitful to ask why you NEVER EVER read of these professional reviewers doing blind listening tests, not ever. And they have been challenged to do so. Ultimately they operate from a position of scientific fallacy in so much as they propose theories that can't be falsified (tested) and therefore fail one of the most important steps used to evaluate if a theory is legitimate. I'm not talking about you here, but when somebody says it is true that I can hear these minute differences because I know I can, well, that is simply foolishness in at least the sense of scientific evidence. I can't test that claim therefore it can't be the basis of a valid theory as it can't be disproven. Not because it is true and thus can't be disproven, it can't be refuted because the interior experience of a person is currently inscrutable and we need to find proxy measures that can be exposed to observation such as well controlled, multiple subject, multiple trial blind listening tests. They aren't perfect and there is error there, but at least it is testable and possible to refine. I can't test the claims of somebody who says trust me, I'm right, I hear that difference.