My wife & I rescued 3 cats shortly after moving into our present home. The previous dwellers abandoned a less than one year old female right before they moved out. She was pregnant and had two kittens (both female) in the woods surrounding our house. They survived in those woods for about a month before we took them in. Fortunately, it was summer. (People like that should be put in jail and/or forever banned from having pets!) So, basically, we took in 3 feral cats. I had a pair of Ohm C floor-standers at the time and, then eventually replaced those with a pair of Paradigm Studio Monitors, also placed on the floor. We lived very happily with our feline children (Maine Coons) for almost 14 years and never had a problem with them scratching speakers, chewing speaker cables, jumping on the stereo rack, the speakers or anything else related to the sound system. We will forever miss them! Of course, trying to predict what different cats will do under different circumstances is virtually impossible. The best advice I can provide is as follows:
A dedicated sound room would be ideal. You could just keep the cat(s) out of that room. However, please be advised that cats are notoriously very, very curious. I've seen some learn to turn doorknobs and open doors!
One cat, alone, can get awfully mischievous. I always think it's better for a cat or a dog, for that matter, to have a buddy. That being said, with cats, socializing them to another non-litter mate can be very, very difficult.
With our feline rescues, I always thought that the minute they heard how loudly my speakers could play that this dissuaded them from having anything to do with them or anything else near the stereo rack. However, I have no idea if this was really a deterrent.
With regard to scratching, our ladies did occasionally scratch at the end of a cloth upholstered sofa we had in the living room. However, a sternly spoken "NO" on such occasions was all that was needed for them to get the point that this was verboten. Hitting or physical violence used in trying to train or discipline pets does nothing other than instill fear and piss them off. Positive reinforcement and/or replacement behavior is always the best approach. Some people subscribe to using a water spray bottle to deter unwanted behavior. We never used this with the girls and I'm not so sure that would have been effective with them or any other cat, for that matter. Cats like resistance when they scratch stuff. It helps them shed the sheaths off their claws and mark their territory. I've heard and read that some people use plastic to cover things like sofa corners, etc., to dissuade scratching behavior or spray natural deterrent scents that cats don't like in areas where they are prone to scratching. Never tried those. What worked with our ladies was experimenting with different kinds of scratch posts impregnated with catnip, which they weren't all that fond of. Eventually, we found what they liked best were corrugated scratch pads for cats. Cheap and effective! They liked those so much, they would often lay or sleep on them!
Whatever you do, PLEASE be kind to animals!