I don't own the Neumann NDH 20 (yet), but I've owned the Focal Listen Pro's, after they've been burned in for quiet some time, and they were way, way too sibilant to my ears. Just bright, lacking sub-bass and mid-bass to some extend and they were also fatiguing - it's so strange, but this leads me to believe that everyone hears things differently indeed (maybe even vastly differnt) and I'd never ever described the Focals as dark, warm, but rather as bright and treble focused. I could not listen to them very long, no matter which source. In comparison, the Denon D7200, Fidelio X2 (maybe you owned either one of them) sound warm to me with non-fatiguing sound.
Also, just as a further example, the Denon D7200 sound rather balanced to me with a really pretty much, to me, perfect signature for acoustic instruments, but there was another site which called them majorly lacking in upper frequencies, making them pretty much not a good fit for acoustic music/instruments what so ever. Some even say the miss a lot of details, which I don't think at all, not even in the slightest.
Just so very interesting...
According to how you are describing what you don't enjoy, regarding freq, i'd say you need to stay with Audeze.
Listen....Almost all "popular" "legendary" audiophile headphones, are bright., except for most of the Audeze products.
The reason is..... when we think about "audiophile listening", ..... this is related to clarity and resolution and micro details, being HEARD.
So, you can't have this unless you have some boosting in the 4-10kHz range, and that means, the trebles have to be a little bit hot to get you that ultra insightful analytical musical experience.
Its just the trade off that you have to accept, if you want to hear ALL the music in a way that is very dissecting.
Right now im digging the Ananda's a whole lot.
But, i dont prefer their sound sig, because it hits the slightly hot treble button to get you what it does best, and that is, incredible detail retrieval.
I still like them a lot, but, its not my favorite sound.
They are a really fine gear, but some are going to have an issue with "brightness".
They don't sizzle the treble, but they do manifest it as reasonably etched and airy.
The "airy" is related to how they dial back the mids just a bit, to get you into their world of micro detail analysis.
I'l give you an example... When you are experiencing audiophile trebles, you'll hear strings being plucked, and a breath being taken before a vocalist begins to sing.
You'll hear fingers on frets, and snares resonating.
Many audiophiles are wanting to hear "it all", so, to hear it all you have to have those trebles just a bit etched. Some would argue that insane clarity is achieved by dialing up the resolution, but i feel that its the combination of treble and higher resolution that gets you there.... as treble is related, sonically, to clarity, and clarity to resolution.
Other audiophiles, want to lay in a sweet bed of sound and be engulfed within sonic beauty, and these types cannot deal with the etched trebles that the other types will accept, for the reasons i stated.
You seem to be the "warm beauty experience" type of listener, so, Audeze is made for you.
And another completely overlooked headphone that is what you would love is the Fostex TH500RP
This is one of those warm snd lush and thick sounding headphones that just wraps you up in a smooth sonic hug., and will never even think about offering a treble that could offend anyone.
You might try it.