I have a backed up movie with 5.1 audio only but I would like to downmix the 5.1 to 2ch stereo and either remake the DVD with just the 2ch or have both. I've read that BeSweet is a decent audio downmixer but I don't know how to re-encode so the DVD contains the 2ch audio.

I should mention its DTS 5.1 for one. I've tried BeSweet but I can't seem to downcode DTS to other types.

Follow this guide at dtsguide site.

Well I have foobar but ffmpeg needs to be installed by command line or something like that. Says I need ffmpeg if I follow the above recommended guide. Installing by command line is way beyond my abilities. Managed to demux the dts track with vobedit and can convert it to either a wav or mp4 file with foobar but after that i'm stuck.

Ok. Found an ffmpegGUI which includes ffmpeg.exe which I needed. Currently recoding as I type this so lets see what happens after this.

Ok. I think I got it sorted out. Demuxed video to m2v and audio to dts files. Using foobar and ffmpeg I recoded the dts to a stereo ac3 file. Using ifoedit I authored new vobs using the demuxed m2v and the new ac3.

Success! Working movie with audio recoded to 2 channel stereo.