Haha, the vacuum takes care of bad behavior pretty quickly, most cats are terrified of that noisy behemoth.
There are some sprays you can put un the floor around the speaker that will supposedly drive them back, but I have no idea how they work. Your best bet is to give the cats something better to scratch than your speakers, like a scratching post and to keep their claws trimmed. That's all I've needed to do with mine, he's never gone after anything else aside from my bed occaisionally if I haven't trimmed his claws often enough. He's pretty easy to deal with, doesn't like to cause trouble, but I've known cats that did so hopefully yours isn't one of them.