This has been mentioned a few times in threads relating to Dolby Headphone. It's a quantum leap ahead of that apparently in sound quality. It mimics the exact sound of any speakers set up (up to 7.1) and is customised for each individuals ears. Therefore the sound quality is totally dependent on the ability of the actual speakers and the room environment in which the measurements are taken. In theory you can duplicate an extremely high end home cinema system through your headphones. It's not cheap, it costs US$3k plus UK VAT and comes with a basic Stax headphone/amplifier.
I'd be very interested in this product except I do not have a good system to calibrate from so would not be getting the optimum performance. In the States, SVS has arrangements with two high end studios where people can go and for a fee duplicate their sound system. I'm hoping they will arrange something similar in the UK (they're based in Belfast and LA) at which point I may invest.
Is this something people here may be interested in?
The SVS site and a discussion thread on AVS can be found here. There are threads on Head-Fi too but I can't access the site!
Smyth Research
Smyth Research "SVS" is finally available for purchase! - AVS Forum