Subwoofer into Naim Nait 5i with no pre-out......

Hi guys I am in a rush to get a cable to take away with me on a trip and am a bit confused. I have a Velodyne optimum 10 sub that has RCA connections and a Naim Nait5i with no pre-out - how do I go about making this work? That is, I need a subwoofer cable with RCA on one end - what do I do on the other and are these cables readily available and if so, where?
I also have a REL sub (that I can't take with me) and how that works is, plug into the Sub (neutric connection) and squeeze the thin bare wire at the other end into the banana sockets on the amp where your speaker cables go.

Thanks