After the problems with the R2 I text here and bought a J afterwards, which was not great either (manufacturing issues straight out of the box on the SE. Plastic ring was squeezed. It was not round and unable tot plug in the 3.5mm jack -> strange isn't it!?). So send that back as well and even after the problems mentioned above I did a last moment of truth to buy the D2.
And yes... no issues at all! The output (which was extemely loud on the R2) is not here. And enjoying it a lot right now. So, I think I found my new buddy here.
In the end guys, I think there was something wrong with the R2 in software or hardware. I don't know. But I am glad to do a last try with buying the D2. Wanted tot let this know. Happy days!