Extremely interesting!

Another thing I noticed: On the Dolby Surround clip, when the audio is collapsed to mono the Alien cue goes from faint to almost completely inaudible. I was listening on my iPhone speaker, couldn't hear it, plugged in my headphones and then I could hear it.

The surround information is carried in the two channels inverse to each other, so the fact that it essentially disappears in a mono fold-down seems to indicate that when the track is properly decoded, the Alien music would have only been heard in the surrounds (similar to the DVD?)