what to do with my cat on my speaker grills

I agree with Wratman, My cat does not scratch on my grills, but I have an extra set of grills on hand just in case he does.

A little aversion therapy. Set the cat up like Alex in A Clockwork Orange (strapped in, eyes held open etc) Inject a little anti-catnip about 30 minutes beforehand. Then just set up a photograph of him scratching the speaker right in front of him. Play beethoven. After a few sessions of cat therapy he'll be unable to scratch the grills without heaving chunks. If that doesn't work move to something more drastic - like cat with asparagus in a light cream sauce.

I see some suggestions for squirt bottles. Maybe a few drops or maybe a tablespoon of lemon juice will help.

My original cat, Renfield by name was plain single minded and mean. I tried the squirt bottle thing and he just sat there and TOOK it. By the time he was soaked, I gave up. Than he came over and jumped into my lap.....soaking WET and purred. He had some other annoying habits, including chasing dogs and intimidating house guests with his rotten behavior.

He never even touched my panels.

Soak the grills with some ugly perfume. Cats noses are highly sensitive.
Repeat procedure every second week.

Make it an outside cat.