I have compared high res download versions with Tidal MQA versions of several albums. (No comparisons with CD quality, or undecoded MQA.) My setup: from my NYC I used USB into my Meridian 818, and from there either Meridian DSP8000 speakers, or analog out to a Bryston headphone amp driving Audeze LCD-3 cans. (Mostly headphones, because of my wife's view of the same track fragment being played over and over.)
Albums include several Joni Michell, Mehldau Blues and Ballads, Metheny Kin, Led Zep 1, Doors Strange Days. 96 or 192. Summary: I found no clear difference. (Which is a good thing, streaming matching my best downloads.)
Some special cases:
Buena Vista Social Club I have a 24/96 download, an MQA download, and Tidal MQA. The two MQA options were identical, the high res download was obviously a different mastering, much darker and less clear.
Magnificat: a 24/352 (which Roon downconverted to 176 because of the Meridian USB limit), MQA 352, and Tidal MQA 352. No difference.
Emerson Lake and Palmer Brain Salad: download and MQA are labeled the same but obviously different mastering, or at least different volume, can't compare.
Ornette Coleman The Shape of Jazz to Come, I had a 24/96 download but the Tidal MQA version was mono, can't compare.
In the limited listening on speakers, I heard some more differences (I had expected headphones to be more revealing), but it seemed there were level differences.
So by this time, I decided to quit and just enjoy the music. I can stream music, for $20 per month, and play it on my system, and it sounds fabulous. The academic study of what's doing what -- nah, not my job.
For example, Crosby Stills & Nash, Suite: Judy Blue Eyes was stunningly good. The details of the quite complex piece came through in a way I don't remember from the last time I listened to it. Which was in 1969, on a crappy vinyl rig, with some chemical mood enhancement. No matter, I love it now.
End of my testing.