I had some trouble enabling sound over HDMI. My mediaPC is connected to a LCD TV via HDMI and - as a rule - there was no sound via HDMI no matter what I enabled in XBMC settings.
It played around with different linux system settings but nothing changend. There are some Wiki-entries about enabling it - they are loooonnngggg, hard to follow - and not necessary, as long, as you use pulseaudio which is enabled by default with most distributions ..
you will find a short and handy description about the problem with pulsaudio that solved my problem in less a minute !
Hope, it will help you too.
Xubuntu 11.10 - XBMC Eden Beta PVR Build + TVHeadEnd Backend
ASUS P8H61-M LE/USB3 + G530
NVidia GT430 Silent
[Hint] (NVidia) HDMI AUDIO
Joined: Dec 2011
2012-01-08 02:06 [Hint] (NVidia) HDMI AUDIO Post: #1
Ubuntu 12.04 LTS Server, Xfce, XBMC Frodo, Skin Aeon Nox, tvheadend tv backend
ASUS P8H61-M LE/USB3, Celeron G530, Geforce 210, 4 GB DDR3 RAM
16 GB CnMemory 300x CF, 1 TB Samsung 2,5" HDD
iHOS104 BluRay Drive, TT DVBS2-1600
Silverstone GD05B Case, Sony PS3 BD Remote control, Logitech Cordless Mediaboard Pro for PS3