Yes it's a tricky subject to design controlled tests , but in case of DAC's we do have prior knowledge .
So it's really a case of whoever claims a diffrence have the reposibility to prove it , not the other way around .
And for audiophiles this migth seems strange counterintuitive and wrong ? Due the separate bubble audiophiledom seems to live in , it's really a small separate subculture, so if you are in that bubble where "everyone" thinks that thera are midnblowing diffrences. A more reasoned aproach can bee seen as herretic on some way (you get banned from other fora for example).
It's like alternative medicine (if it worked it would not be alternative for very long
) you don't see pharma companies defend penecilin and trying to explain why it works .
And in audio you maybe don't need the most stringet test conditions it's not 6 sigma particle physics . so complet oblivion to DUT is maybe not necessary as I claimed .