You can't send messages directly into a poly~ which have some meaning for the poly~ object. As the poly~ object responds to the enable message the poly~ receives the message, not the in object inside it.
The solution is either to do as robtherich suggests, or to prepend a symbol to the front of the message like passmessage (or whatever you like), and then use a route inside the object to remove this symbol.
The same goes for any of the messages that poly~ would responds to.
enable is a generic message for dsp objects. It's the old way for disabling the audio process done in an object. So you can't receive the enable message in the poly~, using Robert's trick is the way to go.