@tholt since you asked,
I have been enjoying my new Abyss for a week now. I am quite impressed with the 1266 CC, it sounds like no other headphone I have ever listened to, and when I listen to it I find that I am unable to do other activities, I am just to invested in the music. Going back to the Utopia or the Stellia right after listening to the Abyss leaves me with a small stage, congestion, and almost metallic vocals. Now mind you if I go away and come back the next day and put on the Utopias first, they sound great, until the Abyss come out haha.
As for amping, the Mogwai SE drives the abyss fantastically, especially when you put in a 5ar4, with my current tube combo the amp does somewhere around 4 - 5 watts into 32 ohms using a pair of Bendix 6384 (6l6gc eq) and a TS 6SU7 the result is really just awesome.
To my surprise, the Abyss also did better then expected on my Kenzie Monoblocks (350mw into 32 ohms). Vocals are nice, but more dynamic pieces miss something that the Mogwai SE is able to provide, this is to be expected. Switching the mono blocks from 1626 power tubes to 12B4As (roughly doubling output power) makes the Abyss quite enjoyable on the monos, and if I did not have the SE I could see using the Abyss on the monos regularly, however my Utopias and Stellias love the 1626 so I don't see the Abyss getting much play time on the Monos.
My only complaint is fit, my ears are to high or my head is to short, so I had to get a headband pad and put it in-between my head and the headband so that the drivers would not be too low. While it is very comfy once on I am surprised at this price that a better solution is not built in for adjusting the height, especially when I see what Abyss has done on the Dianna Phi, though I have not personally warn them, so maybe they are not that comfy once on. Who knows either way they are a keeper, and the Ampsandsound Mogwai SE is a great partner for them.