I really wish I could demo these. Found a great deal on these, but no return policy unfortunately, aside from being defective. Maybe time to read Tyll's review (the harshest one it would seem) again and then decide.
It's kinda funny how this all happened. I've been following this thread, but didn't think I would be getting them. Was looking for an upgrade for my work headphones, but was really just looking for a closed pair. At the same time though, I didn't want to sacrifice audio quality. Was considering Alpha Dogs or TH900/600. Then I brought my HD800 to work and it was amazing even on low volumes. All the details and soundstaging stayed intact even on low volumes, and it felt like I was in another world. I knew closed headphones could never give me soundstaging like that. More importantly, I found no one was bother by the volume level. This opened the door to open headphones. Then I find a great deal on these. To be fair, I could get another HD800 for the same price from Razordog with their 20% off all Sennheiser sale, but it's no fun having two of the same, and I couldn't justify spending $1200 when I could just take the pair I have back and forth everyday (though something I would never do).
I guess my biggest concern lies in how these are with inferior sources, but it doesn't sound as picky as my HD800. Also, these are still relatively new and unproven, unlike the HD800 which has become the bona fide gold standard in TOTL headphones.
Well it sounds like you're taking the time to think it through and put yourself on the right path. It's not a cheap purchase by any means. I don't know why you wouldn't want to just stick with your HD 600 at work. It's an amazing can that hits well above its weight class and you're happy with the results. My honest opinion is the K812 isn't worth the risk of a purchase right now. Even the first run of HD 800s had some undocumented revisions in their sonics before they became what they are today. No reason to think AKG wont look at the feedback and revise as needed. Give it at least another 6-9 months and revisit it.