Since 5.1 channel discrete music surround programs are mixed with full frequency and dynamic range in all channels, including the surrounds (except, of course, the LFE .1 subwoofer channel), it is recommended that you employ a minimum of four matched loudspeakers (L & R Front; L & R Rear) in your listening environment. You might even consider the placement of these four primary loudspeakers as two identical sets of stereo loudspeakers, so that no matter which way you turn, 90 degrees to the left or right, or 180 degrees to the rear, you should be able to reproduce a satisfactory stereo soundstage between any pair of loudspeakers. Your center loudspeaker may be restricted in size due to space considerations, but it should at least match the timbre of your four mains. Further, you should consider recessing the center loudspeaker creating somewhat of an arc between the left and right front soundstage area. If the center loudspeaker is too dominant, either by volume or placement, your left-right frontal soundstage image will be negatively impacted.
For the serious listener, there is the optimum "sweet spot", which should mirror the vantage point of the recording/mix engineers position. It is equidistant from all five main loudspeakers, including the center. Other than this "preferred" vantage point, if the entire listening space is energized with a balanced mains loudspeaker system, then the phase and frequency coherence of the 5.1 channel surround program is maintained. You will be able to move around and never lose the sense of dimension or spatiality.
Placement for the subwoofer, may take some experimentation on your part. In many cases one sub will be satisfactory. However, space permitting, you might consider using two subwoofers in your system. Try using a pair of forward firing subs, placed equidistant between the L & R front loudspeaker. Or put one sub between the L & R front loudspeakers, and another sub, between the two rear loudspeakers. This is really a subjective call and the experts change their minds just about as often.
Amplification should be applied equally to all channels in order to complete the matching, balancing and positioning of your loudspeaker system. We do not recommend the use of dipole loudspeakers, as some suggest, to "diffuse" the surround image. The surround image is created by the mixing engineer, artist and /or producer when the program is recorded and mixed, not by loudspeaker design or placement.
By following these suggestions, you may be able to closely emulate the conditions present during the actual mix of the program. While motion picture soundtrack mixes may not conform exactly to the conditions we've noted here, music surround mixes that require a much higher degree of accuracy, phase and frequency coherence most certainly do.