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.
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/soundfile, 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:  Power Management version 2
Capabilities:  Message Signalled Interrupts: Mask+ 64bit+ Queue=0/0 Enable-
Capabilities: [6c] HyperTransport: MSI Mapping
Enjoy your new digital sound.