I now had the chance listening to the Sennheiser HE1 headphone system, which is basically build up by the new Sennheiser Orpheus headphone coming with a 10 pin connection leading to a sophisticated amplifier based on 8 tubes.
Needles to say it is an overwhelming sound. But what is so special? I always used the same excellent test CD, Rolling Stones, Sticky Fingers, Wild Horses. My different testing models were a Sennheiser HD 850 S headphone with a HDVD 800 headphone pre, my own Sennheiser Orpheus HE 60 with the Stax SRM 007tII preamp modified by some vintage Tungsram tubes (see: Headphones)
The HD 850S sounds clear, precise but also a bit on the bright side. The HE1 and my own system additionally bring more wide and soft soundstage into the picture, the HE1 even a bit more.