just acquired a ksw sub and need help hooking it up, all i have in back of my 5.1 receiver is a rca....what do i do..??? have one speaker wire ( 2 strand, red/black) run thru the wall to the place where i want it to sit, and had an rca plug on it for my old sub...how many wires do i need ...it is quite a hassle to run another wire up the wall and thru the attic then down to the plate in stalled, but will do again if i have too...any help out there,,..???

One RCA "sub out" at the receiver connected to one RCA "sub in" on the sub.

Yeah, there are two ways to hook up a powered sub.

1.  RCA (as mentioned).  Sometimes you need to get a "Y" adapter since the sub cable will be a single RCA out from your receiver and on the back of your sub, you probably have a Left and a Right RCA input.

2.  Line Level Inputs (speaker wire).  You would need to run two speaker wires from the Left and Right channel of your receiver to the line level inputs to your sub, then two other speaker wires from the line level output on the sub to your main speakers.  

Unfortunately, either way in your case, you will need to re-run wires.  I would go with the first option.