Many (but not all) DVD-Audio discs have content that is compatible with DVD-Video - encoded with AC3 or DTS. If you have a disc like this you can get the audio out using DVD Decrypter and various tools - www.doom9.org
has guides - it's rather convoluted. Typically you have to downmix to 2 channels using besweet, you can downmix to prologic encoding and retain some multichannel info.
An even smaller number of DVD Audio discs have straight pcm audio in the DVD-Video accessible content which can be converted to wav or flac or whatever without loss of quality. For SACD there is a CD compatible layer and you can get the 44.1 kHz 16 bit lossless from that - no way I know of the get the multichannel.