See if this will work for you:
Get DGIndex . Under the file pulldown select " Save Project and Demux Video" .
This should give you 3 files .ac3 , .d2v .m2v .
If Nero Wave Editor will edit the .ac3 file to your satisfaction then use it .
Audacity might work as well as some other audio auditing software .
The closer you stay to the length of the original .ac3 the better the sync should work .
Maybe someone else will post a good method of getting the sync exact if the length is different .
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.