Pro Logic problems!!! Please help

Is there any way to get Pro Logic sound when a movie is recorded in Stereo?? I have a 5.1 speaker system and can´t get my center speaker to play sounds. I have installed the newest AC3 filter but that only works with AC3 recorded movies. I get perfect sound when I use PowerDVD but I want BSplayer to do the same. Please help me how I can get sound in the center speaker with a stereo recorded movie.