Yes, however I guarantee you they will be able to pick something out of the mix and fix it and you wouldn't even know it was a problem in the first place. So Mastering Engineers ears suck less.
Excuse me while I am rude about mastering engineers in this context, and ask some different questions about your test (which I have no reason either to believe or disbelieve as such).
Mastering engineers may well be able to "fix" things, but they work in context, as it were. So, they get a recording that has been made in a studio or a live venue, then mixed - sometimes by someone completely different to anyone at the recording itself - then it comes to the mastering engineer, who almost certainly wasn't. The mastering engineer has a particular job - to take the recording, as presented to them, and turn it into either a coherent document for listening to at home (or to be precise, through earphones while jogging or on the train, or on a car stereo, or....) or maybe into a fashion statement (see under recordings with squashed dynamics, or adding massive increases in treble on orchestral recordings, or some of the other "fixes" we've come across when discussing recordings around here).
Do I believe that mastering engineers are/can be good at their jobs? Yes. In this space, we have to believe that much, because otherwise we may as well just give up.
Do I believe that it makes them better judges of fidelity than anyone else? Actually, no. That's not their job, either. They take a recording and make it tell a coherent story, make it listenable, maybe tweak things so that everything is going to be audible for whatever target they have to work to, and quite often (from what we get told by others here) make it sound like a recent hit recording to try to capture some of the same audience. Fidelity to the source often isn't their job, and from our point of view they sometimes have to be very good at getting in our way.
An appeal to mastering engineers as such doesn't help in this instance.
We need to know more about the test. In particular, were these same people involved in other tests, sighted or blind, in the development of your mods, did they have the chance to absorb your sighted preference as a result? Were the tests truly double blind? (I set a higher bar here, in that I only fully trust blind tests where the listeners don't know what is being tested at all - and yes, I do understand that means concern about some of the Harman testing where subjects knew speakers were being tested, for example).
I'm happy to believe that the PS Audio DACs sound different because that matches both measurement, and my subjective experience with them. In any case where sound is actually different, that leaves grounds for people to prefer what I might regard as the "wrong" DAC. I doubt your response when it comes to fidelity, and I like some of the critics here value fidelity, and I generally have preferred products with better rather than worse fidelity. Does that make my subjectivity better in some way? Probably not.
For the record, I did not like the sound of the Directstream, and I rejected some known good speakers when auditioning a few years ago and I suspect that was because that DAC was the source. That's also all subjective as well, I certainly was not blind testing. Of course I'm questioning the result because of my own bias, but also because of a lack of detail about the test.
Unlike some, I'd still question it even if it gave a result that matched my expectations. I hope I've explained why, and that you may answer some of those doubts.
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