The "3D Headphone" function of the in-game settings is surround processed by the game itself which sends that signal to the L/R channel of the headphones, making it sound 3d. I know it sounds crazy, but thats how it works.
Just make sure the sound card is set to STEREO, and all surround features are disabled. No surround settings should be on within the sound card, windows, or on the headset itself, just let the game do all the work. Cheers.