thank you for your quickly answer !
the alt-out option is a very fine solution, but we use an AB168 Stage Box und i will use the LAN transfer to the monitor on stage for aur choir leader.
i have found, that there is no way to select Alt-out to dsnake expander in the ab168, only main-LR pre.
but this is not possible to regulation from the mixer stand
the main problem is, that our choir leader is standing on the stage, this is behind the main PA, so he is not hearing the totally mix.
so he thinks that the voices are to loud or the akkordeon are to soft, and so on
therefor i will test an LR monitoring.
i will test your options, thank you