DCM SUBWOOFER PROBLEM.

Question

I JUS BOUGHT A USED DCM SUBWOOFER AND IT HAS A PAIR OF RCA PLUGS ON THE BACK TO CONNECT TO THE RECEIVER.. THING IS MY RECEIVER TAKES THE SINGLE MONO PLUG.. SO I BOUGHT THE DUAL SET OF RCA PLUGS THAT CONVERTS INTO A SINGLE PLUG AT RADIOSHACK AND TRIED TO CONNECT IT BUT HAD NO LUCK! IM GETTING POWER TO THE SUB CAUSE IM HEARING A STEADY HUMMING SOUND FROM THE SUB. CLEARLY NOT WORKING CORRECTLY.. IS THERE A CERTAIN PLUG CONVERTER I NEED?? THE RECEIVER SAYS SUBWOOFER "OUT" AND I HAVE THE 2 RCA PLUGS GOING INT THE "IN" JACKS ON THE SUB..