I am not sure that the stock tuning of the 1Z is "better" than the 1A really. I think that's a miss-conception that has been in this forum for a while - just my opinion as 1Z owner.
1A is more reference sound than 1Z, and 1Z is more colored (euphonic) sound
I was of similar assumptions, until I owned both and compared 1a vs 1z vs 1z kmod.
At first I thought the 1a was more neutral/clear, while the 1 was more organic sounding.
Then the difference ( with additional direct comparisons to both the Fiio m11 & with ibasso 220 w/amp8 & with tube stage amp ) was that the 1a had more solid state state sound, while the 1z was more analog sounding.
Then the realization that there was a more holographic and bigger soundstage presentation, while the 1a was slightly more artificially flat, similar but not all the way like in between the flat distant ibasso 220, and the forward flat but wide fiio m11...
They had a much more solid-state sound, which the 1a still had, but at least had more holography.
Yet the 1z pulls ahead of them all to have zero solid-state sound and a well laid out soundstage.
These are the cues that separate better gear.
Most top gear today easily have very accurate reference sound, but still sound artificiall in soundstage presentation.
The 1z does not have those issues.
The 1a does still have a 50% that issue.
All other DAPs, no matter how top choice they are, have these issues of soundstaging presentation.
They can try fool you with a distance but still flat & not laid out properly,
OR,
They can try fool you with an artificially created one with use of a tube stage...
Tubes are great for reconstructing lost soundstage, but they cannot bring back any lost detailing or lost ambient cues, so would not be a 100% correct soundstage, which you would note either by soundtrack memory or desktop comparison.
So bottom line is that I am convinced that the 1z had a better firmwares.
That doesn't mean contrary opinions are wrong, as it still is a choice/synergy thing.
But I do appreciate the more accurate soundstage of the 1z, and do not want solid-state sound.