Well, here we go, I'm gonna get into hot water with this one!
To tell you the truth, what you describe is exactly what I heard at the show. On normal recording pieces the HE90/HEV90 combo sounded *really* open, airy and transparent. I had Jude next to me and thought so, and said so, as well.
However...
On a recording, and a voice, that I have permanently ingrained and tattooed "into my skull" - as much as I have the metal bars and tattoos punched into my own, real flesh - that being Amanda McBroom...
I'm going to say that her upper registers, the exact frequency range you described, were "hot". One particular song that I can pretty much sing to myself with my eyes closed - "Only With You" - has a very small natural "sibilance" at the beginning of one word, second phrase:
"Every so often a rainbow
spreads over you"
The HE90/HEV90 combo simply overemphasized the leading "s". If I weren't so married to those albums as a reference I doubt I would have noticed it, for I would not have had the album on hand to play. On classical and lesser known, but very well recorded, pieces the tip up did not draw excessive attention to itself.
The HD600 / HD650 dulled that 's' attack, my (personal) "trial by fire" test (the 600 less so than the 650). When it's right the 's' sibilance is just apparent, like a wisp of rose on a summer day. When just the slightest bit is wrong it disappears or is too emphasized, a true trial by fire - the most delicate of nuances.
The ES-1 / HE90 combo did
not, repeat did NOT, get it wrong. The combo hit the 's' right on the money, which my own system does also (
now that is, for when I lost the MIT's it
didn't, and that drove me crazy. Now it does again). Those few in attendance probably saw me do a double "Thumbs up" sign the moment that system, the ES-1 / HE90 combo, hit it.
For me - me alone - the spectral balance of the HE90 / HEV90 combo did indeed seem slightly tilted up. For most of the classical, and a decent portion of the jazz, pieces that were being used as a reference it simply made the soundstage appear very, very open and transparent. But, like I said, I've been listening to those 3 albums - the 2 Amandas plus
Jazz at the Pawnshop - for almost 20 years on everything from Bose 201's to Martin-Logan Monoliths, 801's, 808's, SL600's, WATT / Puppies and the list goes on until I'm sick of writing it. The HE90 / HEV90 combo...missed it, on all 3 albums.
It was good, but something was just a touch...amiss. And IMHO I've stated what I thought was amiss - the upper midrange / lower treble was a bit too hot. IC change? Could be! Maybe different CDP.
Under the same conditions, however, the ES-1 pretty much nailed just about everything it was given, based upon what I could hear.
YMMV.
[ducks and runs for cover] This ain't a popular opinion but one I felt I heard.