I do not get the obsession with soundstage on headphones. An extra few mm of space around the head is nothing like the 3d space a good speaker system. I have the HD800, and i love the "air" at the top end of the spectrum, but it doesn't give a realistic representation of the 3d placement of musicians like two well positioned and tuned speaker can. Even so, the speaker representation is an illusion anyway. Try listening to a acoustic band and your ears will not necessarily place them accurately with your eyes closed.
I feel strongly the most important aspect of musical reproduction is the emotional message. This is carried by tambre (how delicately or forcefully a string is struck), key changes, harmonic interrelations, and most of all intonation (the rhythmic interplay between passages and musicians). Soundstage is a fascinating phenomenon, while alludes to resolution, but I cannot count it as an important characteristic of musical reproduction.
It is wonderful the first time you sit in front of a pair of electrostatics and hear acoustics from 15m behind your rear wall, but that is just pleasant acoustic pyrotechnics, and pales when you hear the interplay between the piano and double bass when Oscar Peterson toys with the rhythm, or pink floyd teasing at what comes next.
Am I missing something? Enlighten me.