Bright to me means , after a hour or so horns seem sibilant. I find myself wanting to turn the volume down on the Utopias. Switching over to the inexpensive 400i on same track wanting to turn the volume up. Not as good sound. But easier on the ears.
Not downplaying your preferences at all. This isn't in regards to either Utopia or HEK, but it's related to your comment and MH reply that the Utopia's are neutral, which is something I have been thinking about a lot recently.
If you listen to horns playing next to you for more than one hour, to use your metric, in real life, which is the standard "neutral," it wouldn't be very pleasant. The snap of the drum, stroke on the violin, can be piercing IRL.
I actually agree with your point. Most users here who spend multiple thousands of dollars on gear want to use that gear by listening to extended periods. To listen to hours on end without damaging your hearing, you're eventually going to need a tuning that is not neutral or one that is but at lower volume levels. Something like the HEKV1 or HD650 is perfect for this type of listening.
This perception has come into tighter focus for me recently. There is equipment that is brighter than neutral, but there is also equipment whose aim is to proximate the highest fidelity possible. To faithfully translate the real experience of music often involves discomfiting slam, sharp leading edges, natural decay of sounds, the ability to snap you out of attention and lull you to a whisper, small gradations of shifts in volume, tangible texture and bite, etc. What I have found for my own habits and preferences is that I cannot handle this for long periods of time. For that, I need something that does not compromise detail and technicalities but that is still pleasant enough to enjoy without blowing my ear drums.
High Fidelity does not equal bright, but it does not support "unnatural" sustained listening sessions of sizzling violins, cracking snares, or blaring horns bordering on the sibilant. I am finding myself preferring a happy balance between the two extremes as of late.
Finally, what strikes me as highly plausible without having heard them, is that the HEK2 are exactly the kind of transducer I need to try, since it would appear to ride between the two extremes nicely. I pair the Utopia with tubes for a reason.