I see friends with cats and hear about all these problems and see them getting on the kitchen counters and table and to me that is discusting. After having a cat that lived 18 years and one that is now 12 indoor/outdoor I have a pretty good idea what they need and how to train them.
First of all if you have a young kitten, that is when it is best to train them, just like a kid. The one thing I have learned is if you are going to teach them anything you can't try and train them when you are home and then leave them with free run of the house when you are gone. They will not learn this way and you will only get frustrated. What we have done with both cats is given them the laundry room when we are not home, that is where their food is and their box is. They also have toys outside of that room and we use scratching cardboard which comes with catnip and it works great.
When we are home they get to roam the house and when they were young and did something they weren't supposed to they got yelled at and clapping hands and the word NO. This only works if you only give them the chance to make the mistakes when you are there. It doesn't work if you let them free and are gone and can't tell them no. I have been down this road with so many friends because it seems so obvious to me but it usually falls on deaf ears. Both of my cats once trained "which was very quick" never got on the counters, never scratched our furniture and never got on anything we didn't allow them on. Once you've had them for a few years you can even let them out when you are gone and they still won't do anything wrong. I know this from leaving food out that they would definitely eat, like butter and they would never touch it nor was anything else out of place.
Give them a lot of attention and love, both of our cats, which never new each other did not like it if we were mad at them. They didn't like to be scolded and generally want to be mellow and accepted. I have never had an indoor only cat so maybe this is what some of the problem is with them acting up. I would never get them de-clawed, what if they get out? they have no way of defending themselves. Also, how would you like to have an itch and not be able to scratch it?
We have always let our cats out during the day "for short times" and then called them back in. We NEVER let them out at night as we have all kinds of predators which most areas have, not to mention cars.
If you follow the simple rule of not giving them the chance to make a mistake they will learn and then all in the household will be happy and your speakers will be saved.