I'm not doubting the quality of your cables in any way. It's good to know that adding another device in between is unlikely to solve the (minor) issue, and part, if not all, is a known "feature". So, I'll not be spending money trying -and failing- to sort it. Thanks.
I will experiment with a different cable arrangement to see if that makes a difference. It's admittedly a bit of spaghetti coming out of the back of Yamaha, and electricity cabling behind and under the cabinet.
Best wishes,
wnv