My k812 arrived yesterday, and so far i'm pretty much disapointed. First i was blown away, because its beautifully build and sounds beautiful. But then i started to compare it to my k400 & k501 and for me, these sounds better. More organic and alive. But the k601 & k7xx series don't stand a chance vs the k812. I also liked the T1 much more than the k812, soundstage is bigger and sounds overall better for me. And that comes from an AKG-Fanatic ;D we used a Lehmann Audio Linear USB and a Violectric HPA V200.
Also, i was surprised , because the k812 is definetly NOT easy to drive on portables. Me & a friend of mine, we tested it on an ipod video 5G, iphone4, samsung galaxy s3, sansa clip and some tablets. A T1 or any other Beyerdynamic is easier to drive on portables, much louder. K812 is hard to drive, similar to a k601/k701.
I have to listen for a week, to see if the sound improves or not, i'll tel you guys ;D