I think there-in lies the issue for your preferences and sensibilities, personally: You view a linear treble and the resultant lack of crisp, ultra-perceivable detail as a fatal flaw. Considering the amount of mixed reception on this thread already, I think that's an opinion shared by many, and understandably so. Detail retrieval and clarity are extremely common benchmarks of performance, followed by stage expansion, layering, separation, etc.... before timbre and tone, very commonly at the bottom of the heap.
Now, I don't intend to generalise and say any of you necessarily do so and/or are wrong if you do. But, the ETHER 2 to me represents a rising trend in in-ears and headphones (like the Empire Ears Phantom, the JHAudio Layla, etc.) that flip industry convention and place timbre and tone at the very top of their respective lists.
What good is a lively, crackling snare if they all sound relatively similar? Or rather, leave you with similar feelings? Snappy, open and clean on literally all tracks, anything else? These aren't questions I'm personally asking - because as you said, we all hear differently - but these are questions I believe the products and their makers are asking. Now in my opinion, transparency comes in two parts (rather than one as most people I talk to assume): Detail-led transparency and tonal transparency. The former refers to how much raw information (i.e. detail) you can draw from the recording. For most people I've seen, this constitutes about 70-80% of what makes a good headphone.
How much detail can it retrieve? How effortlessly does it do so? How well is the stage structured, layered and separated?
However, tonal transparency is a matter I've rarely seen discussed. Personally, I didn't even know it existed before enrolling into my audio engineering courses. Now, let me reiterate that this does not make me a
better listener in any way - simply a
different one. I'll touch on this later. Anyways, tonal transparency to me is how colourless the headphone is in tone, and the way I determine that is by observing how much it changes from one track to another - specifically, from one track to another in a singularly-mastered album - and find out how much of its own inherent colour is imparted onto the track. Can I determine shifts in staging as
@LCMusicLover mentioned? Does the headphone's inherently (perhaps, stubbornly) large stage make that difficult to discern? If I listen to
Lost in Paris and
South of the River by Tom Misch, can I hear that shift in the saturation of Misch's voice, not to mention the other instruments? If I listen to
Burning and
One Day At A Time from Sam Smith's
The Thrill of it All, can I pick up the subtle differences in the lower-mids or the upper-treble? Is the only meaningful insight I can gain from them simply the notion that they sound clean and clear? Most importantly, could I have identified these shifts as quickly and confidently if I didn't know about them to begin with?
Personally, with the alternative mastering headphones you mentioned, I'd probably find them a lot more challenging. Because, they're not as discerning in tone as the ETHER 2 is. The HD650 has a stereotypically warm bass that remains pillowy at all times, the HEK is coloured in a hi-fi sense to sound constantly clean and crisp, etc.
The ETHER 2 is on the same boat as the in-ears I mentioned, in that it's split pretty evenly between both forms of transparency, rather than the more common
70/30 ratio I implied earlier. I believe this is why reception on it has been mixed: It sacrifices aspects of detail-led transparency in order to achieve a level of tonal transparency that most people aren't accustomed to
and tonal transparency is an often underrated element of audio to begin with. Now, returning to my earlier point, does that make individuals who uphold tonal transparency on an equal plane as detail-led transparency in any way better, more mature, etc.? In my opinion, it absolutely does not. Headphones don't have to be ultra-precise or reference-grade to be enjoyed (or considered subjectively good), and the opposite applies too. This is why I often criticise terms like
Reference-Grade or
Studio-Grade in marketing. Heck, in a terrible, egotistical and callous world, those in the
detail camp would scoff at anyone who could enjoy such a muffled, un-crisp sound, while those in the
tone camp couldn't even begin to comprehend how one could enjoy music with such tonal indifference.
So, what I'm probably trying to say here is that things tend to be more than they seem, context is key and joy is in the bias of the beholder. I hope you've all gotten something out of this splurge, 'cus this is surely more than my
I've-been-awake-and-live-mixing-at-church-for-8-hours brain can handle. Cheers, hopefully nothing I said here causes anyone any offence.