It took me forever but I think I finally figured out how to make a dvd from a mkv file that has two audio tracks, japanese and english! First I use ffmpegx to extract the english sound track using the movie to ac3 button then i use mkvtoolnix to remux the movie with the newly extracted english audio track then i use kigo video converter to convert this mkv file to dvd file that roxio toast can burn to a dvd.