[captaindiego]

If you're willing to mess with audio and have an AVI/MKV, you could extract the audio from the two tracks you want, convert the 2 channel (from the surround mix), then flatten to mono, and put track 1 and 2 into the stereo left and right channels. Then get an adapter that takes stereo and outputs each to a mono 3.5 connector, and then convert that back to stereo for the headphones. You can do this with a mix of mkvtool, audacity, and ffmpeg.. although it is a fair bit of effort. Likely the suggestion from rcarr is quicker