Thanks a lot for your hints!
I now have installed the Linux packages you mentioned.
Unfortunately I can not see which "hardware" I should choose in VLC player as audio output.
Under "Audio/Output/Output Module" there are a lot of varieties appearing.
The same goes for the available number of devices (in the line below).
I've started the all the applications.
In >patchage< VLC is still not appearing.
Maybe it could help to deliver a screenshot to display the whole situation....?
Just some pointers:
Install the package "patchage" and "vlc-plugin-jack".
Then in VLC chose "hardware" as audio output.
Download the JACK-version of Stereotool
Start jack using qjackctl
Start VLC and Stereotool
Connect VLC to Stereotool using patchage.
If that works, you can begin to automate the launch.