Hi I have a BS4 in my main room and a 3500 speaker in another, they connected with masterlink. Yes you can play different sources in the different rooms, cos the radio only has one tuner you can only get one station at the same time.
No problems playing and controlling A mem on my 3500 while the wife listens to cd or radio in the main room.
What top system plus 4gb standard SD cards do work on the BS4 fine.