Got it.
wandering audiophile disease.
see what happens in the pursuit of perfection…lol There were a few analogies with wine in a thread on subjective vs objective views in audio here. Your dilemma may be an adjunct to that issue.
Most often sibillance “lives”within a certain band in a recorded vocal. Engineers use de-essers and EQ etc to minimize this. You hear it. It is there. Whatever the reason, you are now able to recognize it. Casual listeners may hear it but do not recognize it…this goes for any number of flaws in recorded music. Many casual listeners don’t hear into any music. That is pick out individual instruments, timbre etc. An autotuned vocal for example, especially if handled subtly may not bother some or it can drive some crazy! There’s always a tolerance factor.
Anyway, whatever is behind it, you recognize it and I suspect you are subconsciously “looking for it”
Not sure it was mentioned in all this but a DAC with filtering settings may be an answer. I just got a Chord Qutest and am “playing around” with the filtering. It is subtle but as I “train” my ears to the differences….Also the interaction with the Audeze headphones I am using.
I am not familiar with your DAC.
I do think much of your issue may be your ear training facilitated by an equipment change is at least part of it. It is why top engineers always refer to the need for “good ears”