A single RCA cable is needed to connect between the subwoofer output jack on the A/V receiver and the Left or Right line level input on the subwoofer.
SVS offers SoundPath audio interconnects in various lengths, and these work great as a subwoofer cable, and also as a full-range interconnect for CD and DVD players and external amplifiers too.
Make sure to account for horizontal and vertical distances and corners when estimating the length for your subwoofer cable – it’s always better to have a bit of extra than not quite enough.