After you have some time with them try taking off the grills, that seemed to bring out the highs a bit more and make them sound even more open. I also took out the foam that sits between your ear and the driver and replaced it with thin speaker fabric. I'd be curious to see what other people think, I've been running my HD600s like that for over a year and a half now.
I'm listening to mine right now. I don't think that I feel the need to mess with purrfection.