The audio system of your car may be covered under your homeowners or renters insurance. It falls under personal property protection. Check with your company to be sure. No matter who covers (home or auto) document what you have as a record just in case of a loss. As for auto insurance the only way to guarantee coverage is an agreed value or declared value policy. Usually these policies can be quite pricey. Relize also that disclosing performance modifications may dramatically increase your coverage cost even without the declared value option. Depending on you age, location and driving record performance modifications may cause you to be considered "high risk" or uninsurable. Another avenue to investigate is some type of rider policy on either the car or homeowners/renters insurance policy. I have such a rider that covers some very expensive jewelry and a bicycle. Just some different options.