I doubt that the amplifier for the sound system wants to run on 5 olts. my suspicion would be that it wants 12 volts, but that will depend entirely upon the sound system you are using. Best advise I can give is to check the instructions of the sound system, or with it's manufacturer. Annother point to bear in mind is that most ESC's will supply 5V for the receiver, but it is a fairly low current rating, often around 1 amp max. Depending upon the radio system you use, you may be drawing more than the ESC is rated to give, especially if you attempt to power a sound system as well as the radio at the same time.