Xonotic reverts to Stereo sound after having set it to 5.1

Hello, I'm running Xonotic on my Windows machine for the first time, but I can't get 5.1 surround sound working.

Relevant system specs are: Windows 7 Pro 64 bit Creative Audigy 2 ZS Xonotic 0.8.2

When I set Xonotic's channels option to 5.1 it changes back to Stereo when I click on another option screen, start gameplay or when I exit Xonotic right after setting the channels to 5.1 and start Xonotic again. On the console it prints the following error message: Failed to open audio device! (Direct Sound CreateSoundBuffer: invalid parameter) S_Startup: sound output initialization FAILED S_Startup: initializiing sound output format: 48000Hz, 16 bit, 2 channels... 5.1 surround sound works just fine in my other games.

Greets!