Hello RaztoR and everyone else here!
this is my first post, I'm a long time lurker but for this thread I really had to register to get involved in the discussion.
Hopefully my experience can help you at least a little bit.
My background is as a long time audio engineer, I've been working with broadcast almost exlusively for the past 6 or 7 years. Right now in radio broadcast, so a lot of live-to-air stuff.
As troublesome at it can be mixing in headphones are a necessity, so I see were you're coming from RaztoR. Sometimes it just can't be done any other way, whether it is recording TV in loud enviorments, or mixing a show for broadcast at the side of a stage with blasting PA. Headphones is the only option then, and preferably some that isolate well in that situation. For good mixing cans with high isolation I can recommend the Remote Audio ones with Sony MD-7506 drivers:
https://remoteaudio.com/products/hearing/high-noise-headset/
As for mixing long time in headphone I have to agree with LightninBoy, it will get painful... And with closed cans, you will get fatigued from listening in another way than from open backed cans.
I have both Sennheiser HD-650 and MrSpeaker Æon closed (1:st gen) at home, and have been using the Neumann NDH-20 at work. I used to own a MiniDSP HA-DSP which I bought as soon as it launched, but I've now soled it. Quick summary of what I think of the headphones mentioned:
HD-650 - Easily the most comfortable, can be enjoyed the better part of a day since they are open back. Not the most pronounced bass, or any detail really, but the light weight really helps for the long hours.
Æon closed - same with the weight, really helps. Quite tricky to get a good fit, and I've had to return them on warranty for some fault with one of the drivers (it sounded different and lost sensitivity). Very good people to deal with, but the shipping from Sweden-US and back took a while. Extremly comfortable as well but the closed back nature of it gets fatiguing after a few hours. Also, which I wasn't aware of when I bought them is how difficult they are to drive thanks to their low impedance (13ohm nominal). Works very well with JDS Labs Atom or the like, a Babyface Pro FS would be a stellar match.
NDH-20 - Quite heavy cans! I can't wear them for more than an hour in one go, but thankfully a quick break resets the comfort for me. Very good sound, works with ANY amplifier, neutral sound for me, and the distorsion is extremely low. Makes balancing and EQ:ing of sources very easy. The cable that comes with the phones are downright horrible for all the noise that is transported through them to the cans. The cables are also extremly stiff. I had to make a special one to be able to work with them at all, I'm keeping that cable in close possession..
About crossfeed and externalisation plugins: I haven't tried GoodHertz CanOpener but I would like to! Please let me know how they work.
I did experiment a lot with headphone equalization and crossfeed filters when I had the HA-DSP amplifier, but since it wasn't up to the job of driving the Æon I eventually sold it. I have been trying out Airwindows Monitor-plugin with his externalization algorithms, so far they work very well and doesn't change the sound of the headphones very much. Should be a good match if you equalize the sound of your headphones.
Regards,
Fabian