Okay, Guy, I've read this now, but I'm not really following the problem. If multi-channel source material is being played but you have only the two main front speakers then 2-channel down mix is the correct result. If your mains are set "large" or "full range" they'll get all the bass and only LFE(low frequency effects), which aren't present most of the time in movies, would be sent to the sub. If you set a "plus" type of setting for the sub then the sub would also get the low bass which the mains are playing.
