Did you ever get a response to this? I am also looking to implement something similar, I have all my speaker cables coming to a media closet and would like to have the ability to send audio to any room (either for the tv in that room, music, intercom)...
If you got this going, I would be curious to hear how it turned out. Also, what is the make of the multi-room amplifier you got/
The OP was trying to use a Marantz amp of some description...which model is unknown. However if you have the rs232 commands to access zones 2-n in your amp then essentially its just a matter of replicating what you would do manually to select a source and route it to one of those secondary zones. There may be in addition setup steps you need to take manually in the amp to map the inputs or speaker config for secondary zones... these will be amp specific of course.
All the best