<font color='#000000'>What is your question exactly?
This is normal behavior. The 5ES has six amp channels. When you switch on the 3rd room, two of them are used to power the 3rd room speakers. Note that the 3rd room can play a different source than the main room, which is why these speakers need their own amp channels. That leaves only 4 channels for the main room, which is why the centre channel is turned off. Note that the centre channel signal is mixed into the left and right speakers instead.</font>