Weird monaural cord (too small?!)

Alright, I'm aware this is a longshot but here goes.

First off, I don't have anything in front of me, things got a little slow in my office so I decided to try figuring this out once and for all.

Here is my problem: I have a Sony HT-DDW990 home theater receiver system. Everything about it worked fine until once time I moved it around from one room to another and then a few days later I notice that the subwoofer is not making any sound. It's a powered sub which connects to the receiver via 1 rca cable (labelled a "monaural audio cord" in the instruction manual), and that cable goes into a dedicated Sub output on the receiver.

I checked the power and there was indeed a tone if I put my finger on the rca input of the sub. I figured it must be my RCA cable so I switched it with a random red, yellow or white rca cable from my drawer. Here is where I noticed I had a real problem.

One of the ends of the "monaural audio cord" that had come with the system is SMALLER than a normal RCA jack, and it goes into the subwoofer which has a SLIGHTLY smaller RCA input. Meaning, I CANNOT connect my subwoofer to my receiver without this cable, and it seems to no longer work.

Now, this whole deal happened over a year and a half ago. Despite my best googling efforts, I haven't found ANY information on a strange sized RCA jack or the cable or the subwoofer or ANYTHING, even on all the message boards and the tech support sites.

please help!