I really do wonder sometimes what peoples "reviews" of DACs would be if they had no idea where they came from, or how they measured or how they looked or which company produced them etc.
We did a pretty good job of single blind testing for most of our tests. When comparing a batch of DACs, we hooked them up to my Benchmark HPA4 preamp. It has the ability to adjust input levels, so all DACs were the same volume. Then one of us would listen, while the other switched inputs. The switcher would randomly assign A/B/C to each contender, and the listener would ask to change using the letter designations. Not "double blind", because the switcher knew which was which, but we tried our best not to influence the listener.
When we compared notes, we realized that were were hearing the same differences between the DACs. That added much to our confidence in our findings.
I did something similar alone when I recently compared my Cary SLI-100 tube integrated against a Cary SLP-2002 tube pre with one of my solid state amps. I hooked both through a speaker switcher, matched the volumes, then randomly pressed the "toggle" button enough times to lose track of which was which.
Then I diligently compared them back and forth, making note of the differences that I heard.
So yes, it can be done, but you need the test gear to make it happen.