thanks again. Success!
I got it working. It was easier than I thought.
Don't know what happened but as I told you before, everything, besides of the menu was working on the touch screen. So I thought it might have hapened something during the installation process. First I switched off the mouse pointer for the TFT screen. Then I uninstalled your enhanced GUI, rebooted into the original vanilla version. Tested - everything looked (and responded) ok.
After that I re-installed the enhanced GUI and tested it -> now the menu works as expected! Strange, but I don't complain

Now I will install the GPIO add-on and built it up with one or two relays (I have only one amp "behind" the DAC); will feed back when it works.
Thanks again for your time and help. Keep on with your good job!
Raimund