I am losing it or reading things that aren't there!
I was just reading about power in another thread and assumed you meant the power cord.
Sorry, you just need a simple RCA cable. Again, yes you can pick on of those up anywhere or you can get a better one from one of the sponsor vendors at the top of the page, monoprice, blue jeans, or ebay, etc.
They are standard and if you have a short run a cheaper cable will work fine.
They look like (and should be) regular male RCA plug connections. I use RG-6 coax and screw-on RCA plug adapters. Cheaper than anything else, you can get RG-6 in any length you want and it works like a charm. I know the RCA plug it what that Onkyo takes and it looks like what goes into your sub as well.
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