@Gerrit42 just for future interest . do you have a recommendattion of a specific microphone cable good enough for led data transfer? Thanks!
sommer Kabel
kriegste bei reichelt
da sind dann auch direkt 2 daten lieter drin
schirm sowohl am controller und am strip mit minus verbinden !
also mit G/GND bzw - 
DANKE
To all !
Just for thos who are intrested in i have now tried to connect 2 strips to the same Data Pin. I only tried it with a view leds per strip.
The result is that it looks like it worked. the second cable works like a twin of the first cable, so they are synced if you want use this word. Every Led position on both strips act exactly the same way.
Hope that will help .
Your description is exactly as it should work. Anything else would mean a wiring or LED strip problem.