Reddit reviews Premium Grade Subwoofer Cable with Adaptor, 25 ft

You are going to want something like this. This is only to illustrate the type of RCA cable and splitter that you will need. I am not recommending this particular cable, not that there's anything wrong with it. Obviously you will want a RCA cable long enough to accommodate your subwoofer position in relation to your revceiver. Then you need the Y-cable to make the connection to your subwoofer.

You will connect one end of the RCA to your subwoofer pre-out (located just below the antenna section on the back of your receiver..black connection with white box next to it) then on the other end you will insert the cable into the Y-cable female input then the two male plugs go into the R/L RCA inputs (red/white inputs on the top left). Doesn't matter which goes into connector from the Y goes into right or left on the sub.

Here are also some options for cables and a splitter.