I have observed that cats love to stretch themselves out by putting their front claws on your speaker grills. This leaves tiny little runs in the fabric, but thus far no damage to the drivers.
Occasionally, a cat will jump up on top of a floor-stander. Cats, having great power and control ("power is nothing without control"), usually nothing untoward occurs and there is just a cat sitting atop the speaker like a living sculpture. However, I once found an Axiom M60 lying horizontally on the carpet. Fortunately, it didn't hit anything on the way down, so there was no damage, cosmetic or otherwise. The cats left no forensic evidence and wouldn't confess after I read them their rights.