@almarg for the win! I was reading through this post, thinking a DEQX would solve this. I too faced the same issues with “awkward” high end frequencies, too bright, but not consistent. I say “awkward,” because the high end wasn’t consistent on every type of music I listened to. Sometimes it would be inline with the overall track and other’s it would sound “excited” and cut through the rest of the music. Sometimes it wouldn’t be enough. I thought, ok, it’s got to be the room. Had GIK Acoustics build a room treatment setup, based upon my room dimensions and outputs from REW (Room EQ Wizard), which helped, but there were still some weird high frequencies popping through. I toed the speakers in, moved them away from the walls, spent a couple months monkeying around with placement. Then thought, must be the tubes in my preamp. Bought NOS Mullard’s, frequencies still there. Additionally, I had an entire Shunyata setup, power cables and conditioning, then someone recommended a DEQX. Solved. And when I say solved, I mean, it elevated the entire musicality of the system. They are pricey, but can be had on the second hand market and there are folks on here that really know how to squeeze the most out of a DEQX.
Best of luck in addressing it.
Best of luck in addressing it.