CD is based on a digital sampling method called PCM (Pulse Code Modulation). It takes a 16-bit snapshot 44,100 times a second. DVD-Audio has created more options with the ability to do 24-bit samples up to 192,000 times a second.
SACD is based on a completely different technology called DSD (Direct Stream Digital). This uses a 1-bit sample taken 2,400,000 (roughly) times a second.
So at the very basic level of sound card technology, DSD is not even supported. It has only now begun to penetrate the high end recording studios. Even DAWs (Digital Audio Workstations) such as Pro Tools cannot yet record DSD material.
All that said, the first thing we need standard in all computers to play SACDs is for the sound cards to support DSD. I believe that is part of the new Azalia standard others are talking about. Once that becomes standard on PCs, then we will begin to see the ability to play SACDs on the computer.
http://anandtech.com/multimedia/showdoc.aspx?i=2079
