I hear the D8k just as
@betula describes them. I owned a pair and liked them very much, and they're one of the few pairs of headphones i'd consider buying again. To add to betula's impressions, I'll mention that the bass is outstanding, one of the best bass presentations I've heard. Sure the 1266 is tighter and faster. Yes, others have more slam. But the D8000 extends deeply and robustly and has good mid-bass punch. It's also nicely spacious and open-sounding in the bass - much like the Tungstens (I've got an SS one right now) - and the D8k's bass has nice textures and timbral richness.
The D8k is also wonderfully smooth and non-fatiguing. That smoothness has to do with a lack of treble trouble and what I guess is low distortion; while smooth, the D8k doesn't smooth over details, and you get a nice amount of texture (admittedly my DAC then was an Yggy A2, which is great for this). The headphones are slightly rolled off in the treble, enough to impart that slight warm sound, but they're not rolled off so much that they lack treble air and spaciousness. The headstage isn't big, but neither is it small, and the sense of openness and air is wonderful for a pair of warm headphones, which can sometimes prove to be a bit suffocating, for me (e.g. the RAD-0).
With the right amp you can get plenty of impact; macrodynamics are strong. I never had the excursion/rattle problem in the bass with my old pair, nor do I have that problem with my current pair of D8k Pro.
The resolution is very good. Transients are snappy enough to make for a fun, engaging listen without being overdone. The truly wonderful thing about the D8k is that they're the least fatiguing headphones, sound-wise, I've heard.
If I were to win the lottery tonight, I'd get a pair immediately. The Pro version, which I'd been keen to check out, retains many of the qualities of the original, except they have more treble emphasis, which produces a more neutral, ordinary audiophile tuning. Where the D8000 are distinctive, doing their own warm, smooth, fun thing, the D8k Pro gets kind of lost among other similar headphones like the Susvara and Caldera. (I'll be selling my pair of the Pro, fwiw).
The D8000 sounded very nice from my Stratus but better from the Violectic V281. This was a beautifully synergistic pairing. Beware the D8k with the Bliss; the latter's damped quality works poorly with the D8k, making them sound too soft.
Edit: I forgot to note, importantly, that the above impressions were with the pads from the Pro model, which improved the sound, for me.