lots of ways to demux...i think most/all involve ripping the vobs off the dvd so make sure you have enough free space
1) rip vobs: <a href="http://www.doom9.org/software.htm" target="_blank">dvd decrypter or smartripper</a> ....
2) graphedit, here's a good <a href="http://nickyguides.digital-digest.com/audio-extract.htm" target=_blank">guide</a>
3) delete the vobs when finished
there maybe a one click solution, but this works pretty good.