Get a pet store and get some of that spray cat repellant - it shouldn't discolor anything and it really does work well.
Then the cat will use a scratching post instead of your grill cloth.
A little post shouldn't hurt the sound any.
Have you priced that stuff?!!

It was $28 for a smallish spray bottle at the pet store we use! I think I could probably replace the grill cloth for less than that...
In any case, the post is working -- being a cat, she won't scratch it (naturally), but she seems to have stopped scratching the subwoofer as well. Instead, she's decided the two different sets of cat stairs we have sitting around are where she should scratch. Good kitty!

I don't dare move the scratching post, of course...
It's one of those upside-down vee shape types with one side sisal rope and the other side carpet. We'll call it a room treatment and let it go at that.
Our old cats loved those cheap catnip soaked cardboard scratchers, this one is not the least bit interested in the cardboard pad with or without the catnip.