I've not seen CFA in any form, so I can't speak from personal experience. From what I've read here and elsewhere, however, it is not "about 9/11"; rather, it's about the human potential for kindness and compassion. While the tragedy of 9/11 may have been the impetus for the characters' response, the show focuses on that response rather than the actual terrorist attacks.
I agree that this could, on the surface, be a hard sell to those who want to "leave the theatre with a smile on their faces", but everything I've read so far indicates that this is precisely what happens - those who see it leave feeling uplifted. So, it seems that the folks behind CFA just need to position the show carefully. Personally, I don't think it's necessary to mention 9/11 at all in the marketing/advertising; the copy should be something less specific and more philosophical - something with a more "lemons into lemonade" slant. I don't mean that to diminish the tragedy in an way; I just think it's important that acts of terrorism not be allowed to achieve their goal and this show's message seems to be "you won't make the rest of us hate like you do".
==> this board is a nest of vipers <==
"Michael Riedel...The Perez Hilton of the New York Theatre scene"
- Craig Hepworth, What's On Stage