Get a R2R DAP like Luxury Precision P6/Hiby RS6/RS8, which gives a different kind of music presentation. More relaxed but not losing the technicality.
I am keeping my U12t as it pairs very well with my Calyx M, comfortable to wear and a solid reference IEM for checking detail and mix. I do find it a bit bland and on the boring side sometimes compare to Phonix.
If you want to try another level of detail and speed, try electrostatic IEM, like Stax SRM001/2, or Shure KSE.
Check out these two threads, I discovered quite a few things in there. Maybe get an IEM with a complementary tuning to U12T, like Trifecta, Vision Ear Elysium, etc.