Using phones rather than speakers. I'm a bit loath to unplug the hi fi from the tv and connect to the computer (no hardship, but it's a 17 foot room and they're at opposite ends!) but it might come to that.
Green socket confirmed (first thing I did, been caught out by simpler things than that in the past!).
What is puzzling me a bit is that restoring to a three months old Acronis image, when the audio was OK, has had no effect.
That image would have totally reloaded the o/s and drivers to a known working state.