finally i got it to work :)
i used a global variable for each of the 9 possible symbol placements.
when a symbol is created, i store the UID of the just created symbol in that variable,
like in the screenshot in my first post.
then the winline check function determines, which winning line should be activated, and starts the animation of the symbol, picked by unique id.
so if the slot matrix looks like this:
147
258
369
the winline in the middle (258) would be adressed like this:
...
thank you all for your help