Heribert: I do not understand why iTunes should be the problem as it works well in the mainroom. It must be some kind of ML problem.
I agree. Here's a little troubleshooting logic:
1) Other link sources sound fine in room 2 so the ML input audio to room 2 and the BV8-32 is not the problem
2) N.Music/N.Radio sound fine in other rooms so iTunes, iMac, BeoPort and ML output from room 1 is not the problem
Therefore, I'd guess that there is some kind of connection issue between the audio output of room1 and the audio input of room2... although, it's not a general problem because then the other rooms would have issues. Perhaps room1 and room2 go through the same junction box and there is some kind of issue that only shows itself in room2 when the audio output from room1 is active... The description of the sound might mean that only 1/2 of the balanced audio is getting through.
Stan