OK, with the help of you both I got two XP-bars on my screen but sadly it didn't worked as expected. Including into MainHUD had no effect. Including into Custom worked but the second bar was always visible, even at the loading screen.
Data was also only right in the Experience2 window, the normal window showed level 0. The second window had also no options to control.
I guess that thing to do is more complex than I had expected, so I let it be and live with the hardcoded position of the game menu.
Anyway, thx for help