Well, I haven't posted much but I could chime in and give you some insight. I own both the M50's and 580's, and I would throw in with the 580's without a second thought . The M50's are great headphones; I recently gave my pair to a family member to set them off in the land of greater sound. The 580's however, carry the more controlled yet impactful bass and still come through amazingly well in the mid and high range. The M50's begin to dissapoint me when listening to a variety of music. Sometimes the bass is overly apparent and the mids fall back, and I feel as though the high end lacks in comparison to the 580's with orchestrated music. The staging on the 580's is much better and you can sense instrument placement a lot more. I think if you're using even a basic source material, the 580's will thrive.
Then again, like some say you may not enjoy the ultrasone experience. I personally do, and so do many of my friends who have tried mine. I also have replaced my ear cushions on the 580's to the beyerdynamic dt250's velour pads. I find them excellent, too.
The M50's get great hype here, and rightfully so, but i feel more emersed in music when listening to the 580's.
Good luck to you, man!