Maret, if you have enough room behind your listening position for a back surround effect to develop(say at least 4')then a 7.1 speaker setup can be used with advantage. This applies to both 2 channel and 5 channel source material; processing such as DPLII extracts natural ambience present(in varying degrees)in 2 channel material and steers it to the side surrounds and also the part which should be imaged in back is steered in "stereo" to the back surround speakers. with 5 channel DVDs processing such as DPLIIx leaves the front channels unaffected, but processes the side channels to extract information which should be imaged in back and again steers it there in "stereo". Use of two rather than one back surround is suggested both to take advantage of a possible left back/right back difference and to avoid a psychoacoustic "reversal" effect in which a center back sound is instead heard as being center front.
