I went out to lunch with some friends and sat the PSB Speakers M4U2's on the table. They were curious as to how a pair of $400 headphones would sound and so I played eminem's Superman.
My mate said that it was like listening to the 12" subs in his car. He was very impressed. His girlfriend said also had a grin on her face and said they sounded "nice, very clear".
The PSB M4U2's and the Bose QuietComfort 15s share the title "most expensive headphones I own" as they each cost $400.