Thanks for the link. I already knew it and it describes how to play midi using Linux means alsa/timidity). But midi is uncritical since Coyote works as well, as I said above.

The problem is that RealTracks cannot be heard. When starting a song, I can see in the title bar that the Realstyles are retrieved correctly (from my external HD).
In mixed Midi/RealTracks styles only the midi part is then to be heard.

As far as I understood, both, soft synth output and RealTracks are routed to the same audio driver which is in my case MME.