First up, the problem: I have a set of 5.1 speakers that I use when not talking to friends through Steam or during the day. I also have an Asus Vulcan headset, that I use in the reverse circumstances. By default Windows is set to 5.1 output. This causes problems when the headset is plugged in as I only hear the left and right channels, not the rear or centre. If I set the output mode to stereo, the channels get properly mixed and all is well, but it is a real hassle to get into the settings and change everything around every time. The question: Is there a utility out there that can automatically switch the output mode, be that when the headset itself is plugged in or via a simple tray icon? I did a bit of Google-ing myself (I'm not that incompetent, you know ) and found a thing called Vista Audio Changer, but some users reported problems running it on Windows 7. I also found SoundSwitch, but it only seems to change the playback device - from what I have read.
What sound card are you using and do you have the proper driver installed? Windows often uses a generic driver by default, and I find that the manufacturer specific driver has a bit more configurability which might help you with what you're after.
I, err, don't use a sound card. Yet, at least. I might get one in the near future. I suppose it is Realtek HD Audio that I am looking for?
What motherboard are you using? The page on the manufacturer's website should have a link to download drivers for all the onboard components.