Audio amplifiers, including internal sub amplifiers, don't operate at the 120 volts measured at the wall outlet. The transformer in the power supply section steps that voltage down to perhaps 40 volts. Using 120, either resulting in 500/120 for about 4 amperes, or in another iteration of Ohm's Law(E/R)120/4 for 30 amperes, doesn't give relevant results.
The somewhat simplistic calculations above using square root(power/impedance)are adequate to give the poster information as to the currents in effect at various power levels.
