My DX90 works fine (knock on wood), no button issues. My TG334's never sounded so good. I believe the DX90 is a wonderful value. I haven't personally compared it against the expensive AK line but I really don't think they could sound that much better. iBasso hit a home run with the DX90, we are lucky to be living in these times.
Glad you like it, I'm considering one myself. And yes, there seems to be a growing argument these days about the diminishing returns in purchasing the very expensive DAPS, especially when it comes to driving iems at reasonable volume levels.