I didn't claim anything. I have not done measurements of things. I'm simply repeating the results of people who have, people I've literally named. You can go look at those, or you can not. That is your choice.Wait...lol, but I'm the one who's skeptical xD
You claimed, "noise always creeps in". I don't believe that to be true. So, respectfully, why would I spend time looking for evidence that I don't believe exists? If it's easy enough to find, then I would greatly appreciate you linking any of the evidence you've seen to date that shows a commercial DAC's implementation of galvanic isolation was in any way ineffective at preventing ground noise.
And I think you may be mistaken--I don't believe the Gustard X26 Pro has any galvanic isolation. I also owned one, and I did several months of research before buying it. The lack of isolation was one of several reasons why I sold it...
You're claiming anything with galvanic isolation can't produce noise, ok cool. If I had to bet though, I bet the next thing you'll say is, it doesn't produce audible noise, am I right? Yea this isn't ASR, I'm not getting involved in that conversation but I'm sure they'd love to have one with you if you take it there.