If you're using a Pro Amp with a NeoX+ and other inputs that are not going through the NeoX+ you will need to follow the instructions below:

For each room, add an AV path setter driver. 

Connect the Neo audio output to the audio input for the AV path setter.

Connect the audio output for the AV path setter to the relevant input on the MDX.

Set all properties for the AV path setter as above. Set the relevant room to the endpoint.

You will need to add the TVs for this to work.