I have found the problem. It is the directwire from the MAYA.As a double check on MuLab side, insert an audio mixer strip in the modular area and connect its input to the output of that 3rd input module that is connected to rack 7. Then open the mixer strip editor and see if it shows any level. I assume it will show no level either, right?
First picture of directwire shows the situation with my trouble.

Second picture of directwire shows the situation with no trouble. All 4 channels work well. That picture is true.

Third picture of directwire shows the situation with no trouble. All 4 channels work well, too.

When I use the wiring from the second picture, and add a second wire from input 2 to asio 3 , then I have signal 2 on channel 3 AND on channel 2 . It looks like a hidden wire from input 2 to ASIO 2.
It makes me pensive. Is there any other hidden setup menue or file ?
It is not so important, I can work with that.
Thank you for your help.
best regards
