…back from the easter family vacation. And many thanks to Stefano for the tip. And yes, Hao-Lai, that’s exactly how I had did my setup. I think my mistake was much more trivial: I had forgotten to click the “Select” button on the input page of the web interface. 
Curious: The message “failed to connect” appeares - nevertheless “USB Audio gadjet” appeares on my DAC.
And it really works great! Even if it always jerks during auto rate switching for the first few bars - no matter… The streamer always runs the most of the time the redbook format anyway.
So it worked - and I’m very satisfied. Now I can control all my beloved radio stations, my CDs, my music files on the internal hard disk, on the NAS, roon and the Qobuz streaming via the streamer and the great Hqplayer.
Now I will make final comparisons with Qobuz streaming with Streamer, Roon and BubbleUPnP (so far the best performance with Hqplayer).
But now I can concentrate on the other tuning measures, such as cables and power supply.
Many thanks…
Best regards
HH