Read this detailed and well-written guide:
http://forum.blu-ray.com/subwoofers/95817-guide-bass-management-part-i.html
A pertinent passages reads:
"People have a psycological difficulty with the word SMALL. They have spent good money on their front speakers and get insulted when the AVR sets them to SMALL. Remember that this is not a personal insult against you or your speakers. My Definitive Technology front speakers have 15" built-in subwoofers with built-in 300 watt amplifiers. In addition to those, I have 4 external subwoofers in my HT room. When I set the front speakers to SMALL, the quality of the sound (both music and movies) improves. It is helpful to redefine the words SMALL and LARGE to: LARGE = No bass mangement. SMALL = Speakers are Bass Managed."