I use TDA Pro 1.6, and I use MPEG1 for almost every dvd I author. My PVRs encode the audio as mpeg1 (which is fine with me, uses less space). Under the TDA settings, I use "Automatic(Audio Stream 1 only) for the Stream Configuration, and "Automatic (Smart rendering)" for the Audio Output settings. The result is a dvd with mpeg audio.
You may also want to check the default settings, so it doesn't give you any grief. Go to Option, Preferences, Default settings. Uncheck the "Use the settings below as defaults for audio output"