As just mentioned, I’m satisfied now with being able to shut the Rivo down with pressing the power button for 5 s, so I won’t contact the direct support (I did it before because I’m not able to play DSD directly, cf. also The opposite behavior of the DSD settings - #65 by gkkpch), so everything’s okay.
But thanks for your answer; and commenting to your “unfortunately” 
yes, I really like the Rivo, having it as a dedicated streaming transport, and in my opinion it sounds better than my smartphone with the app USB Audio Player Pro, which I used to use before. Also the rare function of using a micro SD card is great with the Rivo.