I've just gotten my new 5.1 set and it works perfectly, except in gw

My setting in windows (vista x64) and in my sound card driver menu are both on 5.1 (Soundcard onboard HD realtek from GA-P35-DS3 with support up to 7.1). When I just start gw I have sound, but no 5.1. When I click on the 'Use 3d sound hardware' option, theres no sound anymore

Can anyone help me solve this?
