hairy_hen said:

Either way, the result would be a 4.1 mix with monaural surround, similar to what appears on the Bluray releases of Alien and Aliens. (The fact that those include their 70mm audio shows that it can be done easily enough as long as proper care is taken.)

Were the 70mm mixes ever properly confirmed as the source for these tracks? It seemed to be the most likely case (what with their being 4.1 as opposed to 5.1) but since the menus and packaging are so reluctant to discuss any technical specifics...