Having spent a whole day trying to sort this and having to do a full re-install after breaking it, I believe the solution to be as follows:
1. install Gnome ALSA Mixer
2. After install open from, Menu - Sound and Video;
3. On the lower left side of the mixer window are a number of check boxes, as follows:
IEC958 Default PCM
Dynamic Power Control
4. Check IEC958 (3rd one down) so that first 3 are all checked
5. Master Volume - this was on minimum, but once sound was working, this seemed to have no adverse effect on the volume.
I trust this may help someone and save them a few hours of heartache!!