Thank you for taking care for m problems so intensly! 
Thank you for posting the screenshot. Everything looks good!
We need you to do some more things and answer the following four points.
Obvious question:
1. Do you have a 5.1 speaker setup connected to you soundcard?
Back to your screenshot: In the window "Lautsprecher-Setup", see the selected entry "5.1 Surround". Click on "Testen" and count the number of audio signals, each signal being played back by a different speaker of your setup. You should:
2. hear six sounds, each coming from a different speaker
3. perceive them at the same level
4. hear the sounds as the following sequence: left speaker, right speaker, center speaker, subwoofer speaker, rear left speaker, rear right speaker