It's got to be a function that the sound card (or integrated chip) supports. Otherwise as far as the system is concerned the headset is the same as the speakers, and muting the output channel mutes both. The Audigy 4 Pro has a breakout box with a headphone jack, and when you plug into it the speakers are muted. The option is configurable in the settings for the Audigy 4 drivers. I picked up one of these for $100 on eBay. You might look in the driver settings for your sound hardware and see if the option is already available. If it isn't you'll need new hardware or some other solution. Maybe someone makes a pass-through box for the speaker and headphone connections that takes care of this.