I dont have any experience with this monitor, but I have done this with my monitor but using hdmi instead. Check for a setting or go throw you menu buttons on the monitor and look for sound options and look for an audio1 or audio2 setting and select the one you have it plugged into, and that should do the trick. Make sure you set it for audio 1 or 2 depending on where you plugged it in.
Have you tried plugging it into all of the audio ports???
Phenom 9850 x4, Asus MVP Deluxe , 8gigs OCZ ddr2 1066, Visiontek 3870x2, Xfi Elite,2x WD Raptors 10k in raid 0,Antec 1000watt, and Cooler-master Stacker 830 Evolution.