After playing around with it on and off throughout the day... so far I'm liking the sound more on the ZSX? Not quite ready to put my name to this claim though. Need more time and testing. So this is just my hot take for now.
The main difference I noticed is that vocals seems a bit more natural sounding on the ZSX. Not sure what's the correct term to describe it. Like it's more airy, and they fall off a bit slower. Whereas on ZS10 Pro it's like very tight and more abrupt cut. Is this what they mean by faster decay? Still learning all those terms. lol. But anyway, that portion of the sound also a bit less bright and a little less harsh to my ears on the ZSX.
Other than that I can't really hear much of a difference liao. Maybe limitation of my equipment and my hearing. haha. I'm a filthy casual, so just using direct 3.5mm output from phone (galaxy note fe) and iMac. Audio files are all compressed audio formats, mainly MP3 and AAC. The tracks I'm testing these on are mostly 320 kbps for MP3s and 256 for those AAC files purchased from iTunes.
Comfort wise the ZS10 pro doesn't protrude out as much and maybe a bit more comfortable for my ears. That slightly protruding top part of the ZSX does press against my ears a bit, so I definitely feel these in my ears more than the ZS10 pro, but it's not uncomfortable for me though.
In terms of fatigue, I think more or less the same to me. I think the cable played a bigger difference for me actually. I got the one with mic this time round since I only had without mic, thinking it'll be nice to have an option if it do need to take calls.
Not sure if i'm imagining things, but the cable with mic sounded harsher and more fatiguing for me, and the volume output is also noticeably lower. At first I was using the ZSX with the cable with mic and thought it's more fatiguing than the ZS10 Pro. But then after switching both to cable without mic, I don't feel a big difference in this area anymore.
Anyway, both are more fatiguing to listen to compared to the Tin T2 (maybe i'll have to try using foam to the ZSX to see if it helps), and soundstage is still a bit wider on the T2. However, on the T2 you're missing out on the bass of course, and the extended highs. Passive noise isolation is also worse on the T2 on the stock tips (both foam and silicone). But I still kinda like the T2 actually. I feel like it's a pair of earbuds that I can listen to for hours.
On the KZs everything is like tight, exciting, fast. It's fun to listen to for shorter periods of time, and I think will present pretty much most genres in a good light. Tin T2 i think shines in some tracks with strong vocals and mids, and does well enough for most tracks, but with more bass heavy tracks, the Tin T2 falls a bit flat. But if i want to chill and relax and listen to some music while working or what, I'll probably still pick up the T2. It's still has good enough highs to me, and i'm not much of a bass-head. shrugs.
So hard to say which I prefer. ZS10 Pro and ZSX are really similar. I'm fine with either of them considering how much they cost, but personally leaning more towards the ZSX for now. Comparing the 2 KZs to the Tin T2... will be harder to choose. I think slightly different use cases for both. But maybe if you point a gun at me and only let me choose one, I might still go with the T2.
But anyway, compared to the ZSN Pro, both are upgrades for sure, and they all work with the C-Pin adapter, so i can use the KZ bluetooth cable with them. haha.
Oh, a mini rant I have is that KZ is still giving the same exact cable as the ZSN Pro, which tangles quite easily. Would be nice if they included nicer cables for their more expensive IEMs. :/