I have used a kind of dirty trick to achieve this. If you make your movie files with 7.1 audio, so 8 tracks, you can configure your computer to output 8 discreet audio tracks, so four stereo pairs. The trick I did was to have silent audio on 6 of the 8 tracks and a stereo mix on two. By shifting the tracks with the actual audio on different video files you can have some movies play audio from outputs 1&2, some from 3&4, some from 5&6 and some from 7&8. Furthermore, if you are using multiple sound cards you can create an aggregate device using the audio midi setup utility that will bundle several sound cards into a single device.
You can do the same on windows, except for the aggregate device part, which you do with another software.
Instructions on aggregate devices can be found here: http://donyaquick.com/recording-from-multiple-devices-on-mac-and-windows/
I only used prores codec on OSX and AVI on windows (virtual dub will help you add the 7.1 audio track to the video files on windows and quicktime 7 will let you do this on Mac, or you can export them with the correct channels and mapping from a video editing software).
Maybe not the solution you were looking for but it can solve your problem.
If the movies do not need to play at the same time and you have a soundcard with a good routing utility like an rme fireface you can actually route audio to different outputs by controlling the sound cards routing via midi or osc.