Enable SPDIF on Asus M3N78-VM Motherboard

Recently upgraded my media centre PC to Windows 7 64 bit. However, like many other people, I had problems getting the SPDIF (S/PDIF) audio to work. After a lot of trial and error it appears that digital audio out on this motherboard is either going via HDMI (the default) or S/PDIF. Out of the box [...]