Is there any freeware/opensource tool like dvd-audio-extractor which will allow me to extract audio from dvd's/vob's and create 6 channel wav files(6 wav files) and then mix these 6 wav (one of the channels needs to be dropped) to create a mp3 file.

I know of BeLight (along with BeSweet to create mp3 from wav files) to create mp3 files though.

have a search on Doom9 for DGIndex.

what you do is load your vobs into DGIndex and then save the project.
it will automaticly demux all the ac3 tracks that are in the vob files you loaded.
then use Besweet to make them 6/2 channel wav/mp3's