Can anyone now shed light on how we need to connect this 218?

If it sits between the front L R and the processor, do I need to make either FL or FL my master? I have my centre as my master currently. Do I need to reprogram G65 or HD621?

If it can sit between FL and FR and G65, how do I stop the G65 playing the TV for instance and start using the 218 to transmit to the FL and FR. My knowledge of setting up Meridian equipment is minimal.

G65, HD621, 5x DSP5200SE, MC200.