Thanks for the help, all. What I didn't mention was that I had the system set up as described, then decided - since doing the surrounds was going to be more work - to stop and listen a while :-) I had no problems, and I'm *sure* I didn't have to fiddle with the volume from the mini. It was only the next day, when I turned the system back on, that the problem appeared, when - theoretically - nothing had changed.
Peter, I do have to crank up the volume on the Yamaha, well past half-way, to get reasonable sound when the mini is set to minimal volume.
Soo, I'm going to:
1) See if there's any problem when I use analogue output from the mini
2) replace the optical cable
and see what happens.
Again, thanks - will post results.
Regards,
David