The powered subwoofer should be set to 85-95 hz.  Setting an SB series soundbar into PS-31 will cut low frequencies off at 80hz; this will give a "clean transition".  Another benefit to setting the ZVOX to PS-31 is that it will allow for more power to the left right and center channel since the amplifier isn't using so much power for bass any more.  

To place the speaker into PS-31 press and hold the Power button and the Volume Up button on the side of the speaker for 5 seconds until PS-# flashes on the display and immediately release those buttons and start tapping on volume up until PS-31 appears.

If you have any questions please call 866-367-9869