In the meantime I had some leisure time for experementing with BIAB and Kontakt. Now I can profit from version 2012's new feature of assigning only single instruments with a specific VST-synth.
(Thank you for that good hint, Rainer!)
So, my general synth is Bandstand, and I can replace easily 1 or 2 other instruments with patches from Kontakt. The result is great! The 'old' MIDI-files with their vast variety of styles and patterns are a new alternative to the RealTracks now! Sounds great and loads faster than Real-styles! The only thing is that I have to invest a few minutes for each song I want to add Kontakt-sounds to. But it's worth it.

I didn't work with RealBand yet. So I can't tell anything about working with RB and Kontakt.

Thanks again for your precious hints and advice!

Ulrich

By the way:
Rainer, I'm living in Baden-Württemberg, too. Near Bietigheim. Interested in sharing about BIAB experiences?