We can't answer that unless you tell us what the overall aim you want from ripping this. Do you want to put the audio on DVD or CD? What format, etc...
After ripping the DVD with SmartRipper in Movie mode, run it through DVD2AVI, which has a MP3 option, demuxing the file at the same time, which will give you a 'project', one file will be the audio file you asked for.
go to www.clonead.co.uk
download claddvd v2.5
rip the dvd, u will end up with .vob video files and a .wav file of the audio.
delete the video files, comvert the wav to mp3 or burn direct to cd
VOILA!!!1