[User 78981]

Got audio working. Some more information to those of you who consider to buy that gorgeous device. This is what I did:

I followed the guide in the first of the links I mentioned in my first post.

Code:

cat /proc/asound/version

is showing, that Advanced Linux Sound Architecture Driver Version 1.0.24 is already installed, hence we don't need to follow all the steps as the guide is pretty old.

We don't need sudo alsaconf
We don't need sudo nano /etc/modprobe.d/sound.conf

Code:

sudo alsamixer

to unmute S/PDIF

Code:

aplay -l

is showing:
**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: STAC92xx Analog [STAC92xx Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
Subdevices: 1/1
Subdevice #0: subdevice #0

HDMI audio in my case is on card1, device 3. That means the speaker test need to look like that:
speaker-test -D plughw:1,3 -c2

In XBMC, within the System->Audio menu ensure you have the following settings:
Audio Output: HDMI
Audio Output Device: Custom
Custom Audio Device: plughw:1,3
Passthrough Audio Device: Custom
Custom Passthrough Device: plughw:1,3

That's all.