[71monaro]

Just a note Richie

Even if you get audio out of your PC on DVI/HDMI it wont work running into your Sony TV when playing anything Dolby Digital (All DVD's and most TV) as the TV cannot decode the DD signal, and It seems there is no fix at the PC end

EDIT: found fault
I go to controlpanel->sounds-> and under playback tab there are 3 playback devices.
1) Headphones - (front jack i presume)
2) Speakers - Analogue out of rear, setup option allows downconvert DVD to 2 channel Test on this gives correct sound out and DD sources work on this.
3) Digital Output Device(SPDIF) - this has no setup option, but a test gives sound to TV via HDMI
then I saw properties and in that there was check boxes asking what receiver was able to decode.
It had Dolby DTS checked.
I unchecked it and retried playing a DVD
hey presto - fixed.