Modded Sennheiser HD555s hands down, I know they seem overrated but I've been through tons of cans in my life, used very high end ones and I have to say the 555s (and even the lower end 212pro) are the best range, lowest distortion, crisp high, deep bass (esp. the 555s).
The 555s are the same drivers has the HD595 so don't buy those, the only difference is the 555s come with a piece of foam to muffle the drivers, all you have to do is open each can down to the speaker and remove the foam and bam cleaner sound. Don't forget it takes headphones quite a few (hundred) hours to fully break in.
EDIT: I know you said headset, most of us high end headphone users use desk microphones or shirt mounted ones you can get from newegg. You're not really going to find "Audiophile" sound quality from a headset.
Can't hear my delta fans over my Death Metal crew
The sound of falling
When the pictures are moving
Between the memories
I Just Found Out My PCs Have A Power Button. Meh, Still Not Shutting Down Club Member #00001