I'm sorry. Maybe I wasn't clear enough.
I realize that Windows 7 doesn't automatically let you play sounds on anything but the "default" system. But my point was that I think there might be some way that you could use the headphone jack to power your computer's speakers while still sending sound to a stereo system through the optical cable. And I thought that I had read about that very configuration somewhere but couldn't remember where. So I was seeing if anybody else knew.
And yes Microsoft are a bunch of morons for not allowing users to use their speaker configurations any way they please.