My son got our old 1988 Impala as a college car. He installed a killer sound system with 6 CD changer and amplifier in the trunk. He needed a new super battery and a heavy duty police/taxi style alternator to get the needed juice.
Even if you don’t play the music loudly, you still need lots of amps. Volts don’t kill your system; it stays at 12 or so. Amps need big cables and power source.