You could, but recall that the policy is basically a list of reasons why they won't pay if they want to be hard-a$$ed about, and the fundamental principle of insurance is "take the money and keep it." IME, their approach is always "you will run out of money fighting before we will..."
_IF_ that clause said "used for compensation or economic gain _at the time of loss_" you might have a case. But it doesn't.
It's an even more grey area if you were to give lessons in your home. An instrument in your home would be covered - but it's explicitly excluded if used in business. And good luck explaining that only one of your instruments was ever used for business, even if it was. They'll argue that any of them could be, "since you were obviously engaged in the music industry."
