Thanks for you reply. So if you crank the volume, your headset gets very loud? Mine doesn't; at max volume, it's sort of "medium" volume. I'd been starting to wonder whether Logitech deliberately muted the headphone jack to prevent us from blowing out our eardrums. But the danger is that I'll blow out my eardrums by forgetting to turn down the volume after unplugging the headset. I already came close to doing that once!
Hmm, I guess I'll call Logitech on Monday and ask about it.