Strangely, I think it is the receiver...
1. I changed the cable 3 times.
2. Sub works if plugged into any other output.
3. Sub is on all the time (turned off auto-on function) and turned volume all the way up.
4. During receiver's set-up, it did not recognize the sub. I forced it to recognize it manually. Receiver then tried to "test" the sub three times and kept telling me the sub was not turned up high enough (but it was on max volume).
Looks like it's the receiver