TMPGEnc does not recognize AC3 audio by default. It requires the AC3 plug-in to hear the audio.
Guides for DVD Decrypter
, extracting episodes/recordings, are on digitalFAQ.com
TMPGEnc products are also not as good as the Womble MPEG editors, Ulead DVDWS2 to author, and both have guides here on this site and/or forum.