I have no idea about fixing your speakers, but can you post pics of them? ;\)

Actually, I don't think there would be a problem with gluing it back in, as long as the damage doesn't extend inside the speaker. Even then, MDF is pretty much half glue anyway...

But before you rush into anything, let other people chime in. I'm no expert.

I am the Doctor, and THIS... is my SPOON!