Hi again @Christian, just to be sure I understand. You don’t use any streaming services at all, right? You’re only playing music stored on the K50’s internal SSD?
And the Fritz!Box (repeater), Tempus, Muon Pro, Origin PSU, and NA cables are all connected in the chain to the K50, to allow either your phone, tablet, or laptop just acting as a controller. And you have the internet coming in the K50, but no NAS on the network?