The first time I ever posted on PS Audio was about the my PS Audio PWD Mk2 DAC failing an independent test of this nature.
Ted replied quite extensively on that occasion. I think we agreed to disagree. It’s the old subjective v objective thing to which there is no resolution of competing views.
It did influence me because instead of ‘upgrading’ to a DSD DAC (cost £6,000), I “upgraded” to an Audiolab MDAC+ (cost £800) from the PWD Mk2 starting point of £2,500.
I just remain firmly of the review that good measurements is a prerequisite before anything else, before any subjective listening observations. That was the prevailing professional approach to consumer audio for many decades, when every review included tests against manufacturer specifications.
That said, I appreciate that valve amplifiers generally measure badly, but the distortion they add can result on a subjectively pleasurable experience. If I want that distortion I can add it to my system using EQ, but my starting point is a flat response.
As noted above, the reviewer pointed to the issue apparently relating to mains noise and the output transformer.
I would add that headphones would seem the best way to do listening tests, and I’ve been told that by speaker manufacturers! Speakers are far to variable and many of them are too bright to start with.