ALL amplifiers, even cheapo AB's, have more power to throw at lower impedance. Super cheap receivers, ie sony, won't work with even a 4 ohm load. The best way to explain it is it works like the output of a pump. The pump is the power supply. As you lower impedance, you make the outflow pipe bigger, and the pump gets water out more easily. The better pumps can handle pumping more water- cheaper pumps start to burn up. Really good s.s. amps can handle 1 ohm loads. Certain "8 ohm" speakers can dip down that low. Tube amps do not like low impedance, which is why you have to be careful and buy a speaker with a stable load. In the bad old days friends sold the carver "amazing loudspeaker" with impedance dips so low that it fried most amps.
