trig42: ... Failing that, is ther a device that takes HDMI in and splits the audio out (ie, HDMI in, Coax/Optical and HDMI out)?
This looks like just what you need:
I've bought (cheaper) stuff from DealExtreme before, but it is caveat emptor!
I wonder if the Pi HDMI interface is the same as an XBox 360?
Something else I came across while looking for this might be of interest to other Pi-ers:
Currently I'm waiting on an el-cheapo version of the same thing (will be interesting to see if it works):
I do trust AliExpress - excellent service. Trouble is they often require quantity purchase. (Not this time - but an Xbox 360 converter from Ali, only $1.65-odd, but minimum purchase 150 :-(. )