if so , why no reviews concluding can’t hear any difference.....we have reached that level of accuracy......obviously there should be severals.....but not one........this speaks against your claim............they always report some differencies...........they surely can’t all mess up the set up.
If you look at the subjective reviews, some report that the ADI-2 FS "sounds better", and others prefer the D90. There doesn't seem to be a solid consensus one way or the other among the subjectivists, apart from a general agreement that they're both very neutral devices. If I was just going by those subjectivist reviews, that would suggest to me that there isn't much of an actual difference, given that subjectivist reviewers tend to prone to highlighting/exaggerating the smallest of differences.
And again, since I own both now, there isn't a meaningful difference between the two, at least to my ears. I think the reviewer's state of mind, level of tiredness on a given day, etc., is likely to have a bigger effect on their impressions than whatever utterly miniscule differences exist.
Incidentally, both the ADI-2 FS and the D90 default to the SD Sharp filter, i.e., minimum phase sharp. I found that choice interesting.