I have a DVD of a play my nephew did at school, & he would like to add his own commentary track to it for a bit of fun. So I have the DVD image on the computer already, & we'll record the track on the weekend, but how do I place the commentary into the VOB file for reburning? Is it possible to do it this way? If I need to split the audio from the video will I lose any quality? I did this on a PC & the quality was comparable to YouTube. I'd rather use my Mac with the right software. I also want to keep the menus as they were. Basically I want to just replace/add the audio track, then reburn the DVD exactly as it was before.

Thanks in advance.