Configure XMBC with Bose surround system

Hello dear XMBC community.

I have a question regarding my audio settings. I run a NAS thecus N5550 with the XBMC module installed on it. The NAS is connected to my tv with a HDMI cable. I have a home theatre system (BOSE V30), but there is no more room for another HDMI cable.

Now when I play a movie with surround sound, my system plays it only in stereo sound. I can't seem to set this right in the settings menu ...

Can you help me with this issue? Help is very much appreciated. If there is anymore information needed to help me solve this, you can ask away.

Thanks,
Geoffrey