Thanks to everyone who replied to my post #5043. I thought to elaborate a bit more and share some thoughts based on feedback...
First off, my only headphone for the past 11 years has been Audeze LCD-2. However, the intimate sound stage has me looking for a new headphone. And honestly, the damn thing is pretty uncomfortable with its clamping force.
Music I frequently listen to: classic rock, jazz, old-school metal, classical (solo piano, in particular, but also everything else including opera), trip-hop
Swapped out my 11-year old Asgard 2 for an iFi Pro iCAN Signature, as I wanted an amp with enough current to drive Susvara and the ability to add some tube sound to HE1000SE.
My chain: FLAC/WAV Roon -->Monoprice USB -->Chord Quest stock filter-->Audioquest Golden Gate-->iFi Pro iCAN Signature
Some listening impressions from the past few weeks:
HE1000SE: I really want to love this headphone. For classical, it is hands-down the best I've heard. For rock, it is so addictive and engaging but listening fatigue can set in after 30-45 minutes. For metal...I still can't get over the treble, almost sibilant at times. For trip-hop, I miss the deep ocean sub-bass of Meze Elite, but the bass of the HE1000SE is quite good - very tight and controlled. However, after ~100 hours of burn-in (I just left the headphone playing music from Roon; I did not actively listen for 100 hours), the treble has not mellowed out, at least to my ears. That said, "tube" mode on the iFi has tamed the treble a bit, but brighter recordings are still *bright*. Guess I'm more sensitive to treble than I previously realized.
Susvara: solid all-around but not as engaging as HE1000SE. Vocals are recessed in comparison and I'm not as involved in the music. I feel the Sus is too "polite" for me. And classical, especially solo piano, is too holographic for my taste on the Susvara.
Meze Elite: too laid-back. It is beautiful to look at and so comfortable and so well-built. And that sub-bass is beyond any headphone I've ever heard. But for classical (solo piano, especially), it isn't even close to HE1000SE. And vocals across all genres are too recessed and veiled. I feel disconnected from my favorite tracks. Could I fix with EQ? Perhaps. But I am no expert and feel that I can find a headphone having stock tuning that matches my preferences.
Dan Clark Expanse: I could not get over how sensitive these were to ear placement. Slightly shifting the cups dramatically altered the sound signature. Having slightly compressed pads also had a big effect. Too touchy for me.
Focal Clear: nope. Took one listen and...nope. Not for me. The soundstage is too intimate.
Grado GS1000X: nope. Cold and analytical. I can imagine a recording engineer would love these, but it's not what I'm looking for.
Based on all this listening, I've come to one major conclusion: I want a sound signature closest to HE1000SE, but the listening fatigue is just too much. However, I do want the forward vocals and clarity, especially for classical. And I could do with some deep sub-bass ala Meze Elite. Therefore, I'm considering the following as next to audition:
ZMF Caldera
HE1000 Stealth
Anyone with the HE1000SE end up preferring the Caldera or HE1000 Stealth? Unfortunately, looks like HE1000 V2 (non stealth) is hard to get these days...
The other option is to build around HE1000SE. As others have pointed out, perhaps replace the Qutest with an R2R DAC and the iFi Pro iCAN Signature with a tube amp (Feliks Audio Envy is the one I'm currently considering) and get some copper cables? Or just get the RME ADI 2 and learn how to do some basic hardware-based EQ?
Based on my observations, any thoughts about the best direction to go? Thanks again for your time. This community is really fantastic.