buzz, I think you've got it.
There is ZERO reason that any cable, be it RG6, serial digital, CAT5, even speaker wire used as line level wire, would make a subwoofer "woof" connected from the ANALOG output of an A/V receiver to a subwoofer's line input.

I think Mac's being terribly inexact in describing what happened and how he wanted the wiring to be done. If you read it again you'll see he doesn't mention just what was actually connected to what. And it really does sound like his intention was to run a digital signal to a sub.

But buzz has got it: A piece of RG6 connected to the LNB input of a satellite receiver at one end and connected to the line input of a subwoofer at the other end would, with many non-genie DirecTV receivers, "transmit" a "signal" that switches every few seconds (Mac doesn't tell us how often it "woofed") from 13 VDC to 18 VDC. Older satellite receivers did this to try to get an LNB to respond. I believe that some newer models that are SWM-only don't send out DC.

Line level signals are in the range of a volt. Can you imagine the subwoofer NOT going nuts if fed a voltage that switches from 13 to 18 volts DC?