Why am I only getting partial sound from my 5.1 Channel speakers?

During Surround Sound broadcast of a 5.1-formatted disc all the speakers will not play at the same time and the Subwoofer will only transmit during "large" or "big" sounds. If you are listening to a CD or a radio station that is broadcasted in Stereo sound only 2 or 3 speakers may play. To adjust the sound system so all speakers play, change the audio output format to 2 Channel/Stereo or Downmix.