The third surround channel can be decoded at the cinema's or home viewer's option for playback over surround speakers located behind the seating area, while the left and right surround channels are reproduced by surround speakers to the sides.

To maintain compatibility, the back surround channel is matrix-encoded onto the left and right surround channels of an otherwise conventional 5.1 mix, so no information is lost when the film is played in conventional 5.1.