Just got my HE1000 today.
It's only been a small amount of burn-in time, but I can certainly tell the difference from initial plug in. Less sibilance, tighter bass, and airier presentation.
Only build quality issue I have is the left swivel is not as tight as the right swivel, causing it to easily swivel the left ear cup vs. the right. Not a large enough problem to issue an RMA, IMO, as the headphones will primarily be on my head and not swiveling. The fit of these headphones is superb, and I'd personally rate the comfort above the HD800. I find the HD800 a little loose on the headband setting that fits my head. Any smaller settings and I feel like the driver is too high on my head. No such issue with the HEK, and it was literally made for my head size on the smallest setting.
I love the HD800, but really didn't like the HD800S. I felt like the HD800S didn't have the treble sparkle that portrayed an expansive and impressive soundstage. I also felt like the HD800S had an unnatural sounding bass for the music I listen to. The HEK is what I would have wanted the HD800S to sound like. A pair of headphones with HD800-like soundstaging, a warmer envelope, and some kick@ss bass!
Haven't done an in depth comparison on the Stratus vs. the LAu with the HEK, but I can say that they both drive the HEK to a very pleasurable level. Perhaps that's next after the HEK has had about 90 hours of burn in.