I haven't acquire a cable to make that pairing happen yet. Dragging my feet a little bit there. I do have cables for the Senn 600/650/700s though. When I first got the Mjolnir I couldn't get over the feeling that the thing is just boring. Yes it has authority and slam and pace, and is clear and concise and doesn't do much wrong. But again, I felt bored. So I wavered back and forth with it and the Sonett for a while. Then as I settled in, the Mjolnir became my daily driver digital set up (with 600/650), and the Sonett (usually w/800s) was my special night analog rig set up. I feel there's something about DNA's tuning or voicing that makes me feel like I'm listening to real music more than a recording and I really like that, but for listening hours on end the Mjolnir and 600/650 is pretty great.
How well the Mjolnir matches with the HD800 is wholly dependant on the source component IME. I find the M51 to strike a good balance with this amp/headphone combo.
That said, the MJ/HD650 pairing is freaking awesome. Really special synergy going on there.