Possibly. But the difference could very well be caused by preconceived notions of the two DACs, or somethings as silly as a lack of accurate volume matching.
Yes, that definitely could happen. But one person's bias doesn't nullify another person's bias. If he takes a blind test and aren't able to hear a difference, then there can be two possible conclusions: "There's a high risk of there being no audible difference, or he was biased towards not hearing a difference". But if you took the same test and also couldn't hear a difference, that only points to one conclusion: "There's a high risk of there being no audible difference". Doesn't matter what bias the naysayers have. The person who claims to have an ability is also the one who carries the burden of proof.
I'm not going to demand any proof though. Anecdotes gonna anecdote.