I have several discs that have a fair amount of bass, Pitch Black, Castaway, etc. If I turn the fronts, or surrounds to small, then turn them off, bass below the cutoff freq. goes to the sub. Same setup for center, all other speakers to large, nothing comes out the sub (except for the occasional LFE) Since the center gets a very significant portion of the signal, there certainly is content below 150. In fact, if I set the xover freq. to 150 in the fronts, I can hear male voices in the sub.
Mike