I've read about VOB passthrough mode, but I can't find any options like this on DVDFab v18.104.22.168
On the DVD to DVD menu (left side) I see: full disc, main movie, split, customize, customize split, clone, merge, write data. Subsequent pages/menus don't have it either. For example, Main Movie -> Next gives me the options for choosing copying of video_ts and audio_ts folders, removing DTS audio.
I've also looked in the DVD to mobile menu which shows: Generic, iPod, PSP, Zune, NDS, xbox360, PS3, cell phone, PVP, PDA.
In dvdfab options I have it set to output to a folder, not a writer.