Ok all, I'm now the proud owner of a Chord Mojo powering Sennheiser HD800-S's !
After demo-ing most of the cans recommended here and on other forums.
This simple combination does it for me.
If you're a bass heard (some Triton owners are) then the HD800's and HD800-S's probably won't do it for you. Mind you, these are brand new, so might take time for the bass to open up more.
But the mid range and high's really do it for me and they're really comfortable to wear.
The Mojo's designer really prefers the Toslink input (RF and galvanic isolation etc) over USB (unless you have galvanic isolation of the USB like Intona etc) so I use an optical cable direct from the iMac (which takes a 3.5mm optical plug). The Mojo is stated to eliminate all incoming jitter and PC noise is eliminated by the galvanic isolation of the optical connection. So no noise, no jitter makes for a really easy and high quality desktop setup. There's only a single downside to the Toslink connection via the iMac - limited to 24/96 so anything above that get's down-sampled. In my case Roon is doing the down-sampling and I'm fine with that.
The Dac/amp has enough power for the volumes I listen at. I've tried it with big and powerful headphone amps and didn't find a dedicated amp was needed for the volumes I listen at.
This really blows the Oppo PM-1 and HA-1 setup that I had, in terms of high freq detail.
I may get an Intona or Olimex USB isolator (the latter recommended by Chord's Dac designer himself) and use the microUSB connection of the Mojo, to enable DSD upsampling via Roon.
The thing I love best (besides the comfort and high freq) is that the overall balance from low end to high freq is exactly as it is with my Tritons setup. I get a lot of people telling me to turn my subs up higher but that's just the balance I like lol. But the bass levels for these cans (with the Mojo) are dead on perfect for how I have my Triton subs set, without any EQ required. Couldn't be happier.