EverettT has pointed you in the right direction, altho I use rca to rca for the 1.4V input on my Crown XLS 1500s without issue, you may not need the .775V setting.
Keep in mind the direction of the signal. Your avr has no subwoofer inputs (unless it has a multich input for use with analog outputs from a dvd/bluray player or similar). The relevant connection in your case would be the subwoofer pre-outs (outputs) on the avr to the inputs on the amp (Crown XLS has a choice of rca, xlr or 1/4" inputs).
As far as connecting the driver to the terminal in the sub cabinet, you can use pretty much any handy speaker cable as the length is short, I use whatever's handy, 14g, 12g, etc. That is what I was wondering if you were asking earlier.
Summarizing for your avr to Crown amp rca to rca coax cable.
From Crown amp to sub if using speakon connectors at both ends, just use appropriate gauge speaker cable/wire with the speakon connectors.
From driver to the speakon terminal on the sub cabinet...pretty much any handy speaker cable (if you're getting 12g for the longer length, a bit of this will do just fine).