DVD Audio?

[yaten]

You can NOT play these discs on a CD player - everyone needs to understand that. However, with most avex releases (i'm only going off of the ayu, BoA, and m-flo DVD-As that I own) you can play them on a standard DVD player.

For releases that feature 5.1 mixes, you will need a DVD-Audio player - either one designed specifically for that purpose, or a DVD-Video player with that functionality built in. Even though most DVD-Video players can playback 5.1 mixes on movies you buy, they cannot do this for DVD-Audio unless designed for it, because it employs a different standard.

Please see the wikipedia article for a more in-depth and babbly explanation, if you want:

http://en.wikipedia.org/wiki/DVD-Audio

edit: Also, some cars such as the Acura TL and RL feature surround-sound DVD-Audio systems as standard equipment.