Not sure where you got 2.7, but lots of software players don’t handle the lossless DTS-MA tracks very well. A lossy AC3/Dolby Digital track is pretty universally playable. In my experience, VLC has no problems with multiple audio tracks, but that’s not on a Mac. You should simply be able to select one of the alternate AC3 tracks to see if it plays back without distortion. I suspect you got a remux – i.e. not the original files, probably extra compressed and put on a public torrent. Those are pretty common, because the real deal involves huge files that people generally don’t have the patience to download.
I got it from the ultimate introductory guide to harmys Star Wars trilogy despecialized editions. Each of the films took a couple hours to download and were around 20 GB each. Is that right?