I've tried a lot: PgcDemux, DVDDecypter, Smartripper, DVDLab Pro. They all came out of sync.
It happens in about 10% of the DVDs I am presently demuxing from my discs.
The demuxed audio is always AC3 in this case, as I want to preserve the 5.1.
In once case, if I am not wrong, I did demuxe with Procoder which does output wav 2-channel and it did come in sync, but I am not sure now if it was so. Perhaps I should try it too.
One thing I did think was playing the original disc on my DVD player and capturing it, which would probably work for the audio. But that would also get me a 2-channel wav file.