Eric, the full DPLIIx expands two or five channel material to seven speakers. Since you don't have a 7.1 setup, DPLII is what would be used to expand 2-channel material to the side surrounds, as described in my previous reply. For 5-channel movie material just the regular DD or DTS would be used, because there aren't any back surrounds for DPLIIx to expand the side surround material to.

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Enjoy the music, not the equipment.