the motherboard features the Realtek ALC898 audio chipset with the following audio support:
Support for X-Fi Xtreme Fidelity® and EAX® Advanced HDT 5.0
High Definition Audio
Since you are getting surround when running tests but it swaps over to stereo when running a game it suggests that you do not have the correct settings or that the game does not support surround sound like previously suggested by users in this thread.
Please check all settings and make sure the games support surround and if you are still having issues then please let me know.
Have a nice day and good luck!
Med vennlig hilsen
GIGABYTE Customer Care Representative Sweden