iFi ZEN Stream

[hardcore]

I searched already for optical USB cables here in Germany, I think this could solve the problem.

Yes this cable is unique, because it is specifically designed for 'audiophile' use. Other optical USB cables have a copper power line going from source to destination, which doesn't provide galvanic isolation. This cable requires separate 5V power at the receiver end. In this way you have complete galvanic isolation including the ground and power lines. It sounds amazing if you use a good 5V power supply at the receiver end.