All right, thanks for the info. After quite a bit of effort, and learning way more A/V initialisms than I ever wanted, I found that what I was originally trying to do just won't work. The audio out from my TV's OTA NTSC tuner is PCM, not DTS, AC3, PL2, meaning it would only ever have 2 channels, so there would be no centre channel to disable.
However, I found an arguably better solution. I found this little program called
Radiodelay.
It worked perfect the first try. Select the input (e.g. line in from a radio tuned to 960 AM), a slider to choose a delay (0-20 seconds), then the output device.
It might take a little tweaking to get the audio delay
just right, but i think it will be worth it so I never have to listen to Hughson/Simpson call a game ever again.