What do you mean by a "seasoned" sub cable?
What he means is that you should ignore him because he's really talking way beyond what your setup needs or should care about at all. Your equipment is very much normal consumer gear available at your typical local electronics store. It's not high-end tweaky gear that confuses people and doesn't work right half the time.
I would stick with the Marantz (Denon) AVR.
Set up the AVR with fronts and center set to 'small'. Set the rears/surrounds to 'NONE'. Hook the subwoofer up to the 'SUBWOOFER 1' Pre-Out connection on the back of the 5013.
RUN THROUGH THE TEST TONES! This will ensure that all of your speakers are playing back audio and connected properly. This should always be performed to ensure everything is good.
Set the subwoofer crossover, on the Marantz, to 80hz.
Turn the subwoofer crossover knob (Low-Pass) on your subwoofer all the way up. This allows the AVR to do all the crossover work for you.
Make sure the power lights are on, on the subwoofer. Typically you will hear a sound from the subwoofer if you plug in or remove the RCA cable from the back of the subwoofer.
The Polk subwoofer is really inexpensive overall, so it failing isn't really a huge shock. Subs are one of those things that I really think you get a fair bit of what you pay for. The sound difference between a quality $200 sub and a quality $1,000 sub is huge. Unlike, say, the sound difference between a $300 AVR and a $1,000 AVR.
If your current sub isn't working... Get a good sub.