Been looking at $2k+ headphones recently, and I was considering both ZMF offerings and the HE1000SE (gave up on trying to get the Tungsten). Been having the itch to upgrade from my Arya Stealth that I have owned for about 2 years now. My Mjolnir 3 is paired with a BF2/64 at the moment, and I have been enjoying it more than my Burson Soloist 3XP. I listen to a little bit of everything, would you say I would be better served spending a little more on the Atrium or the Caldera vs a HE1000se?
They are all very different sounding headphones, but I like all three more than the Arya. If you like your Arya, the HEKSE would be the obvious upgrade path. Especially since HiFiMan's big price cut these are good value. They offer the same spacious, and tall soundstage familiar from the Arya. Resolution, refinement, detail, coherence are all better than the Arya.
ZMF headphones are a completely different breed. Neither the Atrium not the Caldera will be as spacious as the HiFiMans but they bring other treats to the table which make me love them more. ZMF sound in general can be described as thick, weighty, organic, lush, slightly warm with great bass. Atrium with its dynamic drivers sound very dynamic with big bass and good 3D staging. It is close, but resolution is a bit behind the HEKSE and Caldera. Still the Atrium has many fans as it is one of the most organic and enveloping headphones. The Caldera is my favourite ZMF and one of my favourite headphones ever. The ZMF planar has that last bit of sub-bass extension the Atrium is missing due to its dynamic drivers. There is weight, impact, clarity; planar speed with the natural and lush organic tone and timbre usually known from good dynamic driver headphones. It is less spacious than the HEKSE, but the image is more focused and separation is excellent. Also, remember that with ZMF headphones you have several fine-tuning options with a selection of earpads and meshes. If you don't like the headphones with a certain type of earpads, you might love them with a different pair.
In a nutshell to me HEKSE and oval HiFiMan headphones in general sound large, spacious, but also a little bright, thinner and diffuse to different extent depending on the model. ZMF on the other hand sounds weighty, thick, lush, organic,
alive. As always, YMMV.