I recently received 4 pairs of (supposedly T400-sized) earphone tips with memory foam from
this vendor. To my surprise, they fit and stay on the ZS3 quite well, even though the ZS3's tip is noticeably thinner than the KZ ATE.
Regarding sound improvements/differences, they made a noticeable difference on both the ZS3 and the ATE but on the ATE the difference was greater.
The ZS3 seems to have become... cleaner. I was expecting its bass to become more pronounced as it already bled a bit into the mids with the stock tips but to my surprise it appears to have a lost a bit of it's bloat and as a general result the overall presentation is cleaner. It isn't a day-and-night difference but it is sufficient enough to be appreciable.
The KZ ATE with the new ear-tips though were very surprising. They already were a pair of IEMs I appreciated immensely, with their more neutral sound signature, but jumping to that straight from a session of listening with the ZS3 emphasized their, by comparison, colder presentation and a bass that seemed much less impacting, or even noticeable, in some cases. When I placed them on my ears just before falling asleep and hit play my eyes shot wide open when I was greeted by a nice "thump" in the bass that previously wasn't there. While they still maintain their relatively neutral signature, they now have a bit of bass that helps make everything just slightly nicer to listen to. When you add that to their impressive (for the price) imaging and detail you get a package that I can't honestly find any major faults with.
I'm still waiting for the ZST, and although I use and appreciate the ZS3 (I'm wearing them as I type this), the KZ ATE's quality and my appreciation for them went up a significant notch yesterday. If the ZST are even better than the ATE, as some have reported, that makes me even more excited.