Q. How much better is 6.1 or 7.1 channels than a standard Dolby Digital 5.1-channel setup? Am I losing something by not adding the additional one or two back speakers?
A. The vast majority of movies are mixed for 5.1 channelsleft, center, and right front channels with two side surround channels. Some more recent movie releases make use of the "6.1" capability, and more recent A/V receiver processors will extract extra information to feed a pair of extra rear speakers on the back wall even if the movie is just mixed for 5.1 channels. There is no question that 6.1-channel or 7.1 setups improve the sense of surround envelopment and also make for smoother and more convincing directional panning effects for side- and rear-mixed sounds, although the room will also influence the degree of improvement. Coverage of surround effects in larger rooms will definitely benefit from the extra surrounds at the rear, and using multipolar surrounds like the QS8 or QS4s will enhance these effects. Certainly there is no downside to utilizing the extra surround capability if the A/V receiver offers it.
Q. If I do add the extra two speakers at the rear for a 7.1-channel system, should I use direct-radiating speakers like the M2 or M3 or the quad polar QS8s or QS4s?
A. In a general way, it's best to use rear speakers that are identical to the surrounds at the sides, although there is some controversy about this. Using identical surrounds at the sides and rear guarantees the same tonal balance and dispersion traits from all four surround speakers. However, many Axiom system owners report excellent results using QS8 or multidirectional surrounds at the sides and two direct-radiating M2's at the rear.