Sorry for the delayed answer but I have been out of town and have not had access to internet in a few weeks.
The motherboard is a desktop motherboard, a ITX board. I have powered the motherboard with a M2-ATX DC-DC powersupply which gives 150W. This powersupply handles the power on and shutdown functions itself via the powerswitch header on the motherboard.
In princip you could use a PS/2 mouse as such as a volume controller but as I wanted to have a more OEM look I made some changes to the mouse so that I get the OEM volume controller feel / look.
I canīt really pin point a tutorial how to make this volume control, but here is one link:
$10 volume knob fabbed.
Basically what you need to do is find a old PS/2 mouse which has got a rotary encoder on the wheel axle and replace the encoder with for example as I did with a ALPS EC11B encoder. The Alps EC11B encoder has got a in-built switch so with this you get both rotary movement and push movement. You donīt need any drivers for a PS/2 mouse but Girder or Volumouse is needed to make the fabbed mouse control the volume. I can post my Girder configuration file here if you want (I canīt now because I donīt have access to the file in my car).
If I forgot to mention something please ask.