Thanks Wheaten,
I have now contacted the manufacturer.
the friendly support from nanosound told me that I started at a wrong point.
Here are the installation instructions for the nanosound plugin on volumio 3:
NanoSound Volumio 3 support – Nanomesher
Will check tomorrow the result…
Is there any hope for the NanoSound CD plug-in to work in Volumio 3? The webpage says dependencies are missing in Volumio 3:
At this stage, Nanosound CD does not work with Volumio 3.x yet, this is due to VLC dependencies not available in Volumio 3.x
I’m interested in NanoSound CD because the built-in CD player in Volumio has issues that make it unusable.
Plugin works after install.
This nanosound pi switch cap is such a great solution for remote, on/off and OLED.
… but after installing autostart plugin and playing some local music files, OLED stops to work. it only shows a volumio picture. remote and on/off is still working… 
I’ve had enough of it for now. maybe i come later back to this issue.
I think the problem is that the complete script is build with Python while loops, instead of using Bash or JS.