I don't think that the question was about anything under X11... It's about Terminal.app, which is not an X11 application.
I also have been very frustrating by its inability to send the Control+Meta combination. As far as I can tell, there isn't a *single* terminal emulator that runs under OSX capable of sending it. My everyday work requires me to use a console emacs through an ssh connection, so being able to type it is very important. (The alternative is to a highly unergonomic need to press ESC every other keystroke!).
If anyone figures out a fix, I'd *love* to hear it!
[In the meantime, I'll try that X11 trick. It might be the next best thing...]