Dolby 5.1 sound can be heard through standard stereo headphones. The mind can perceive the sound in all directions around the listener's head. How is this 3D audio perception acheived with only two channel audio? And only two speakers? Maybe I just don't understand stereo audio well enough. Here's a link for an example: http://www.holophonic.ch/archivio/testaudio/Cereni%20-%20Holophonic.mp3