Take a look at
www.frontx.com - you can have a plug in up front for the
headset (and much more if you want) with a cutoff. When no headset is
connected it plays through the speakers normally. When headsets are plugged
in, it plays through them and cuts out the desktop speakers (Just the
right/left). Set up a profile on the soundcard software for "games" to use
only stereo sound (if you have a X.1 speaker system) and you're all set.
Fitz