>I'm guessing that the impedance is so high that >current flow drops.
Yup, my "load" on the amplifier was my sealed subwoofer system. These systems exhibit a varying impedance that peaks at the system's resonant frequency (as opposed to a vented system, where the impedance is at a minimum at the resonance frequency). I did my tests around the resonance frequency, so current draw was lower than what would be measured at frequencies further away from the resonance frequency of the system.
