==The speaker(load and circuit) does generate it's own electrical (inductance, resistance) signals that are introduced to the output loop of any amplifiers circuit. In low power ANY back EMF significantly affects the pprimary signal. This is usually ignored, but exists nonetheless. Since we are talking high efficiency, we are talking low power regardless of amplifier power.

The reason people biamp triamp whatever is to maintain direct connection to an output circuit to avoid the problems of passive components in a circuit (yes this has been done since amps and spkrs were invented). It always maintains ultimate possible clarity and provides for better control of the spkr. Most of the time this is an effort to increase dyanmic range and power output capability. You can always go passive but it's not -better-.

TC