Do you want all of the audio streams on the dvd or just one audio stream from the main movie?
Assuming you just want one, you can rip the dvd to the hard drive getting just the main movie and select the audio stream you want. You can do this with DVDShrink in reauthor mode, DVDFab Decrypter or DVDDecrypter in IFO mode.
Once you have this done, there are several ways to get the audio separated from the video stream. Since I have DVDLab Pro, I'd just import the dvd into it and select Join and Demultiplex into elementary streams. The result would be one video file and an audio file. The audio would be pcm or ac3 probably. I don't know what format you want the audio to be in, but you can convert it if you have to.
There is a fully functional trial of DVDLab Pro if you want to try it this way. Start with a Simple Movie, use the little folder icon at the bottom left to navigate to the Video_TS folder of your dvd, click on VTS_01_01 and you'll get a pop-up window asking what you want to do. Select Join and Demultiplex.
Another way would be to take the ripped dvd and turn it into a mpeg file using Vob2Mpeg. Then demux in TMPGenc using the Mpeg tools in the drop down box under File. Choose Simple Demultiplex. Both Vob2Mpeg and TMPGenc are free programs.
None of this sounds particularly easy, but it can get the job done. I'm just trying to help using tools I normally use, but for other purposes. Someone around here will probably chip in with a simpler solution---I hope.