I am connecting a passive pioneer DVC sub-woofer (wired in series to generate 8 ohm) to my pioneer VSX-D814-s AV Receiver. As instructed in the manual, I am connecting it to the Surround Back output putting the R+ to the +wire of the sub and the L- to the -wire of the sub. Further I have configured the SB SW and SW ON etc settings as suggested in the manual. However there is no sound at all in the sub. I have cross checked the sub and its wiring are working fine with another amplifier. Can someone please help me configure this sub. Thanks.