Very interesting documents. It sounds like, in theatres, the surround channels are played back through a crossover, the bottom end is sent to the subwoofer, with the low-pass filter set at 80Hz.

If you apply a similar filter in software, you should get the LFE channel (DTS call it the subwoofer channel). Technically, you'd also get any surround channel information under 80Hz included in this audio. I don't think this is too much of a concern, but you could improve the separation if you treated the surround channels as a stereo track and applied a non-centered audio removal filter (basically the opposite to a karaoke voice removal filter) before running it though the low-pass filter.