I have just heard my HD600s with dolby headphone and the line between speakers and headphones is beginning to grow thin. I mean I am hearing just as much visceral impact as speakers impart but I am beginning to notice a much smoother transition with front and back sounds and that's just using a plain dolby surround track from bonus star wars disc Empire of Dreams.
I am hereing the same kind of infront music positioning to sound closer to my speakers while speakers make it sound closer to the screen and even at that somewhat shifted.
Infact its as if my speakers recreate a much more infront and hollow presentation, while the HD600 with dolby headphone brings it out closer torward you and into focuss, even dialogue sounds more centered while on speakers it sounds off center.
The HD600 is a good reference phone for dolby headphone but that doesn't stop there since the DT880 is supposed to be a step up.