Thenk you very much for your effort. I don't see the high gloss level you mention. E.g. the chairs were already mat. Strange that this shows different on your screen.

With Yafaray the results are not better, I already tried that. And I don't have the option for advanced settings on my renderingsettings. How come? Is that why I can't find the invisible hemisphers?

About the lights you are right, but they were not definite yet.