Great news. The Yamaha THR10 works like a charm using Manjaro Linux. The amp has a USB interface with which you can use for recording (e.g. with audacity), but it can also be used as Audio output - it has full range speakers. Everything worked plug-and-play. No single setting nor command line command had been necessary.
Thanks Manjaro . I read about problems using other distros, where you had to recompile the kernel or so...
The Kernel I am running is 4.14.56-1-MANJARO