For me there's better stuff out there, but this is all preference. KZ's don't fit well for me and I own the ZS10 pro myself. Too sharp in treble for me. I love the Truthear Hexa and it does maybe 80% of what my modded 6XX does on tubes, but with the difference that subbass slams much harder and deeper and that there's much less stage and less natural timbre.

Diminishg returns kick in after 200-250ish $ IEMs I feel like, but I move in the sub 100$ area myself. Still wanna try stuff like the Timeless or blessing 2 one day though. I'm sure especially the technical capabilities excel on the higher end stuff.

Now for headphones it's a little different I feel like because what they excel at varies a lot. Some say the HD6X0 lineup is worse then the HD800 lineup, but I would say that they're on a similar level, despite being different in what they excel at. Many things out there are for different tastes and if you don't value certain capabilities of a pair of headphones then they might be not worth it. I personally do not appreciate a huge soundstage as much as I appreciate natural sounding vocals and instruments, that's why I'm plenty happy with my setup. And if you look at the price difference then it gets quite insane, with the HD800 being so much more expensive than the 6XX.

But then someone else would probably say that I'm missing out on a lot. But for me this is not the case. You see, "endgame" is just where you feel like you're satisfied and the only thing that's left then is the fear of missing out, driven by YouTube reviews, reddit posts and advertisements.

So you can simply stop at any point in time and enjoy your setup. It will rarely happen that you will suddenly hear different things in your favorite songs after spending a certain amount of money on a solid pair of IEMs or headphones. Most stuff you can buy is just great and many things are super affordable for what they offer.