I am afraid that I don’t follow your reasoning. If he were to purchase the inexpensive DAC, he owns it. He can then do comparative listening over what ever period of time he chooses. There’s no better way than direct comparison in one’s own audio system.
Charles
Yeah @charles1dad ^that^ works.
The idea of hearing the voices of the angels in a shop, and having that be representative of what one would hear at home is a bit hopeful (IME).
A shop has a total advantage with the room, the content, etc.
But when two units can both be shown to measure well, then it is doubtful that there is a lot left to hear.