Some people may not hear a difference between DACs, like the guy in the review. This is fine. We don't all get tickled by a Rembrandt, appreciate pricey fine wine or enjoy a fast car. Just because you don't hear a difference, though, doesn't mean someone else cannot hear a difference. These types shouldn't impose their subjective reality and perceptions on others.
By the same token, some people may hear a difference between DACs. This is fine, too, for the same reasons. But again, just because you can hear a difference, it doesn't mean someone else can hear a difference. These types shouldn't impose their subjective reality and perceptions on others, either.
Jason Stoddard has alluded on occasion to a continuum, from "no difference" to "day and night difference". I would add to this that people may be hearing differences between DACs consciously or unconsciously. Traditional ABX blind testing requires conscious perceptions, the capability to immediately spot what is different and point a finger. I reckon that people who fall into the "I may not hear the difference, but I enjoy music from my Bifrost Multibit more than I did with Uber" category are most likely perceiving differences unconsciously; they would definitely not be able to point a finger in ABX DBT, which doesn't mean a difference doesn't exist or is not perceived.