Digital SPDIF sound via fiber cable on Asus M3N78-EM (nVidia MCP78S)

 
I have bought Asus M3N78-EM motherboard for my new HTPC. I'm currently testing it with KnoppMyth R5.5 and installation with KnoppMyth R5.5 worked flawlessly.
 
Motherboard specs:

Socket AM2/AM2+ - AMD Phenom™ FX / Phenom / Athlon™ / Sempron™

Integrated NVIDIA GeForce® 8 Series GPU with HDMI/DVI/RGB

Realtek® ALC1200 8 -Channel High Definition Audio CODEC with optical S/PDIF out port at back I/O

NVIDIA built-in Gigabit MAC with external Realtek PHY

1 xUltraDMA 133/100/66/33, 1 xExternal SATA 3 Gb/s ports 5 x SATA 3Gb/s ports (Use SATA1-3 for IDE mode.), NVIDIA® MediaShield™ RAID Support RAID 0,1,0+1,5,JBOD

 
After installation:

Onboard Nvidia 8300 GPU worked

Analog sound worked

Gigabit ethernet worked

 
Only thing that didn't work was digital SPDIF sound via optical (fibre) cable.
 
To enable optical sound you only need to edit etc/modprobe.d/sound file, it needs to have this line:
options snd-hda-intel index=0 model=6stack-digout
 
sound chip on this motherboard is MCP78S as seen via lspci -v command:
 
00:07.0 Audio device: nVidia Corporation MCP78S [GeForce 8200] High Definition Audio (rev a1)
Subsystem: ASUSTeK Computer Inc. Unknown device 82fe
Flags: bus master, 66MHz, fast devsel, latency 0, IRQ 21
Memory at fce78000 (32-bit, non-prefetchable) [size=16K]
Capabilities: [44] Power Management version 2
Capabilities: [50] Message Signalled Interrupts: Mask+ 64bit+ Queue=0/0 Enable-
Capabilities: [6c] HyperTransport: MSI Mapping
 
 
Enjoy your new digital sound.