Concordance with a hypothesis does not prove it.
What is meant above is that, formalistically, a hypothesis can only be disproven, not proven. Once a hypothesis has been subjected to every test imaginable over time, it is widely accepted. Same for a scientific theory (which term is being misused here).
When a theory has survived for centuries, but is later applied to a wider range of phenomena than was dreamt of it sometimes is found to be an approximation (e.g. Lorentz contraction).
Then there is the issue of thinking you have solved everything in a field of inquiry but are wrong. My best example here is in comparative anatomy, which has been a dead field for decades. No interesting research could be conducted because everything was known. Eventually the field transmogrified* into something new (biomechanics, which introduces physics to create a realm of functional biology). You can imagine the widespread horror when, just a few years ago, a gross anatomical structure was found that had previously gone undetected (for centuries or millennia, depending on how you count) - AND in the most heavily studied animal of all, the knee of the only extant hominid species. How could THAT have happened???
My point is that while we have quite good approximations of electronic effects on SQ, we have not conducted a thorough search of the state space with DBTs to warrant a comprehensive claim that every DAC or amp sounds exactly the same or has "perfect SQ." Whether someone is insane enough to spend $10,000 on some oddball unit is another matter of course.
* sensu Calvin & Hobbes
And the ASR reference is a nice touch too. 
