In reply to:

so, i should take one of the two leads i'm using now and connect it to the other port on the receiver, and simply leave the two connected to the sub as they are since only one will be active?


No. That will possibly results in a bad hum from the sub. Say: "NEVER LEAVE NO DANGLING CABLE NOWHERE!"

You need only ONE coax RCA cable (or use only ONE in the pair), which should go from the SUBWOOFER output of the receiver to ONE of the line-level input on the sub. No more connections.