I used my Elegia daily at work for a couple months…the sound is neutral accurate, at least to my ears…a little dry. A warmer DAC amp combo helps some…I’ve used the 789 with them and while a great amp it is also a pretty dry neutral amp(not a bad thing) when I use the Elegia with my Cayin N6ii dap I enjoyed them more, I also really enjoyed them with my NiBL, the burr-brown DAC added that lil bit of warmth to the Elegia, same for the N6ii adding a bit of warmth.
Mind you, these are very small changes, but help with synergy.
The Elegia are great headphones, very technical, but not the most engaging, due to the neutral and dry nature, but that is my opinion. I’m a fan of the Sennheiser sound, but only currently have the HD800(sdrmod).
Based on your statements on preference I think the HD6XX would be a very safe bet for a purchase. As far as at work use case…maybe Campfire Audio IEMs? I’m not the biggest IEM guy but I found the Campfire Audio IEMs to be my favorites and the have good quality and pricing across the brand.
For closed back, depending on isolation needs…ZMF would be my suggestion for a “wow” closed back that is inline with what I’m assuming is your preference in sound. You can look for some of their b-stock closed backs or on the used market to see about getting a set at a lower cost.
Realistically, closed backs are tough, my favorites are well beyond your implied pricing minus the Elegia
1: ZMF Verite Closed
2: Focal Stellia
3: HD820
4: Focal Elegia
5: Campfire Audio Cascades (bass boys)
6: Fostex TH-X00 ( semi-open)
Another option…have you looked at wireless ANC headphones? Sony WHxm3, or Sennheiser momentum? Those are great options for work headphones but you have to deal with charging…depending on use.
Hopefully, that gave you some rabbit holes to go down.
Proof of my work setup…