Many subwoofers accept both line level (RCA jacks) and amplified inputs (+ and - speaker terminals). The Pioneer SX-316 does not
offer line level output, only amplified outputs via the PURPLE + and - speaker terminals. This means that in order to use any subwoofer with an SX-316, the sub woofer will need to accept a + and - speaker wire connections for input Your manual speaker connections are on page 11 of the manual which can be found here: http://www.manualslib.com/manual/260358/Pioneer-Sx-316-S.html#manual
Starting at the rear of the SX-316
; run a speaker wire from the PURPLE + and - terminal (SUBWOOFER) to the + and - speaker input terminals on the subwoofer
. See your subwoofer manual or experiment (at your own risk) with connecting the speaker wire from the SX-316 to the subwoofer's + and - LEFT only, RIGHT only or BOTH left and right speaker inputs. Do not connect wires from the SX-316 to the speaker OUTPUT terminals of your subwoofer.
Finally, adjust any variable low pass filter knob or setting on the subwoofer to the lowest frequency that your main speakers are capable of producing. If you're not sure what that value is, try setting the subwoofer to 100Hz and judge how it blends with the main speakers. If it seems a little too bass heavy and thick then reduce the setting to 80Hz. On the other hand, if the sound seems to be slightly thin and lacking weight, try increasing the setting to 120Hz. By careful listening and a bit of patience you will be able to get the sound to seem balanced and well blended.