I’ve got a pair of Ultrasone HFI-580 cans at home, the review for which will be appearing soon, and I can tell you that they do sound great. They really seal around your ear, though, which some people like and some don’t.
These much lighter (and cheaper at $109) HFI-15Gs are open-back, meaning sound and air pass through the headphones, although I wouldn’t say it “escapes” from my experience. It uses some of the same tech (S-Logic, a surround sound technique) but has a smaller driver, resulting in the loss of 10Hz at the low end and 2KHz at the high end (range 20Hz-20KHz). I’ll compare them to the more expensive 580s and whatever else I have at my disposal when I get my hands on them.