Hi Peter,
Indeed I used to have the MCP9000 but not anymore. However still I have the special converter (Used to connect my BC8500 with the AV9000) which by the way is almost as the standard one!
Since I had no problems with the BC8500 you think it should work under the same condition? But my problem is that if I link it to the rest of the house, when I press radio will my BS4 switch on as well? The only thing I need it to be linked on the rest of the link is for the N.Music and N. Radio. Especially for the N.Music I have the playlists with all the favorite songs of my daughter and definetely will not dissapoint her.
Should work since the BM5500 has the Atape2 command and it will be handled through the BS4 which is my Audio Master.
A bit tricky I assume 
But I'll find the way!!!!! 