this works surprisingly well! Thanks!
I tried to take a screenshot at the end of the shufle process, sometimes a bit hard to tell which one is top/bottom, but especially 1/2/3 are relativly easy to guess.
For anyone wondering, there is a typo in your matrix, it should be
6 3 1
8 5 2
9 7 4
...but if you got the idea, its obvious, but maybe someone was confused...
Thanks for the tip :-)