You might want to try it this way :
You'll need to demux the audio and video streams from the dvd-video.
Get DGIndex .
Under the file pulldown select " Save Project and Demux Video" .
This should give you 3 files .ac3 , .d2v .m2v .
The tool I would use to adjust the sound is Audacity, a free audio editing program. You can find it here: http://audacity.sourceforge.net/
Get the 1.3.13 beta, and get the ffmpeg and lame libraries as well. http://lame.buanzo.com.ar/
By using the ffmpeg library in Audacity, you should be able to import an AC3 audio stream.
At this point you'll want to import the AC3 file into Audacity and follow this guide for amplify & normalize from your audio stream. :
Once you have normalized the audio , click on File-->Export and save as an AC3 file. It will need to be 48khz to be dvd compliant and no more than 448kbps.
I still have the 1.3.12 beta version installed as I didn't know the newer version is out. I will be updating to it but have no reason to beleive the older one would work better.
Now you need DVDAuthorGUI.
File pulldown / Add New Title... It will ask for the .m2v first then the .ac3.
Then File pulldown select Author DVD.
I would put the DVD files in a new different folder on your HDD. The movie name usually.
I would just test to see how the sync was with a player like VLC or MPC-HC. From the HDD.
DVDAuthorGUI does have a Edit A/V Delay which can be used positive or negative time .
After you view & listen this could be used to adjust the sync by repeating the process again.
Part of this information is from t0nee1 & Kerry56 with some addition by me.