I posted some info on the new audio formats available on Blu-Ray and HD-DVD over here:
http://forum.dvdtalk.com/showthread.php?t=451099
The gist is that there are two new multichannel, lossless sound formats, Dolby TrueHD and DTS-HD. I think the general consensus is that neither would provide much improvement in sound quality over the already existing DVD-Audio and SACD formats. The only advantage would be the additional capacity afforded by the new media.