You don't have to look to solid-state electronics for a reason to question, only the first law of thermodynamics. The device is consuming electrical power. It must therefore be generating an equivalent amount of energy. Nothing in the device is moving, I would assume, so there's no kinetic energy. There's probably a few LEDs or something producing some light, but not much. Hopefully there's no non-visible EM radiation, or at least very little. That leaves heat. But you'd assume that that would be the same for both stereos.

Are you sure you measured the current properly? You have to break the circuit and put your ammeter in it in-line. Was the JVC hot when you measured it? How long does it take to get hot?