You can read earlier in this thread that they did not change much through the firmware updates. They just added some bug fixes and the eco mode - that`s about it. Unfortunately
. Don`t think there are any advantages of the older firmware, its just buggier.
About SQ - from what I have experienced in this hobby there are only
very few examples that a maker has truly changed the sound of a DAP via firmware. It has happened so many times in this forum that people stated they hear a difference after a firmware update, but then the maker itself raised its hand and negated, that this cannot be the case. So I doubt that Hifiman has changed anything here...but of course in they end only they know.
Not to say that I wouldn`t be as happy as you if there was an update!