What are you using to power them? Amp/DAC combo? Amp? Desktop Motherboard audio? Laptop?

Are you using PEACE APO EQ?

Ive had no issues with the X2HR on my Fiio K9 Pro's treble or any of its sound qualities on my Little Dot Mk2 tube amp, or the THX 789 amp I have. I'm running PEACE APO and EQ on Windows 10. Currently my K9 Pro is hooked up via USB.

I did however change out the pads on my X2HR with Dekoni suede pads as they are far superior both in comfort and sound to the OG stock pads. Maybe that has something to do with the fact I've had no treble or other frequency issues?