(I had some return tracks on the picture… - the tab was just closed…)
But I could make it work now
H O O R A Y ! 
When I was setting up everything like you said I was like “well, that’s almost where i started, before asking the forum…”, but instead of (de)activating the reverb-effect via my midi-controller I tried it with the “send-button” on my monome… so just one button did the trick
silly me.
I now see that on the one hand I was thinking too complicated and on the other just dumb… Maybe a result of way too less sleep (to protect myself against embarrassment, lol)
Thank You Very Much Dear @elquinto & @jasonw22 For The Hints & Helping Me out! 