I must be lucky that my cats have never troubled the hi-fi. I braced myself when my ex gave me a kitten years ago. Fortunately he was more interested in scratching the flocked wallpaper in the lounge than the driver surrounds of the big old Heybrooks.
I was lucky to be there when he readied himself to launch onto the turntable (lid on, not playing). I threw my cluttered keyring near him onto the floor & have never seen a cat leap so up & back before or since! Sudden, loud noises from an unexpected quarter are the best thing to deter cats IME. If they know it comes from you they learn to continue their behaviour if you’re not around. I found a water pistol to be ineffective in this regard.