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Unfortunately, you can't read the MLP audio tracks on a Mac. You'll need to rip the lower-quality AC3 tracks using MacTheRipper or similar, then convert them to an iTunes-readable format (try mAC3dec).
 
I've had pretty good luck using DVDxDV to rip the audio to AIFF. The interface is really crappy, but it works. Not sure if it's worth paying for, but I heard you can just set your clock back when the trial expires (shhhh! :p). Just make sure you select the right audio track if there's more than one. You can preview them, and usually the surround sound track will sound like the mix is way off, while the stereo track sounds ok.

I've used this to rip audio from a couple of DVD concerts I have. Then I used Sound Studio to break up the AIFF into separate tracks. To get the track split points right, I played the DVD in DVD Player, using the back and forward buttons to get the timestamps of track starts. Then I went into Sound Studio and inserted markers at those times (Insert -> Marker). Finally did Edit -> Split By Markers to split it up into separate files. Then they're ready to import into iTunes.

That reminds me, I still gotta do the split step on a new DVD I bought over the weekend. ;)
 
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