The SQ change after every updates has always puzzled me too...
I had first started noticing these differences back when I had the sMS-200 Ultra.
Some of these upgrades, while clearly introducing a difference in SQ, seemed to never be unanimously "better"...
Sometimes they seemed better" at some aspects of the overall SQ, while perhaps changing other aspects, and depending on what the initial test tracks were, people would form one opinion or the other regarding SQ.
To me it seems that software goes hand in hand with the hardware and as far as updates go, they seem to influence the delicate sometimes balance in our systems and Sense 3 is certainly no stranger to that phenomenon.
Thus, the nature of each sequential update is not without its own controversy and manufacturers seem to have had acknowledged that.
That explains (partially) their hush-hush approach about going public with SQ improvements.
Another thing -not entirely unrelated to the point above- that also seems to apply here (and is especially true of "source" equipment) is the vast variation in systems and rooms streamers play into.
As for Innuos, this comes from the horse's (N. Vitorino) mouth regarding the Sense 3 upgrade: "...With Sense 3, the main changes in terms of sound were done for ZEN/ZENith Next-Gen only to make the most of the new architecture. We have a few improvements that we are testing for all systems. Do mind this is hi-fi, so it's all very personal and what some will consider an improvement, others may not. It is what it is. Every upgrade in our software is to both elevate sound quality and the user experience" (source:
https://community.innuos.com/threads/sense-release-3-0-0.104/).