If I recall correctly there was some sort of hack involving winDVD released awhile ago that made it possible to extract the music from the dvd-a to multi-channel wav and then encoding it to surround ogg or something, but it was rather cumbersome. Might have evolved since then though.
And the DVD-A can not be decrypted by the standard de-CSS hacks, since it uses it's own copy-protection system (CPPM). A quick check at wikipedia says that "As of 2005, CPPM has not beencracked. However, tools have been developed that will patch into a commercial software player and use it as middleware to decrypt the contents of the disc."