oldric said:
transistors will sag under load.
This is not accurate. Transistors don't 'sag under load', - power supplies do that.
Transistors under load have a rising junction temperature proportional to the current flowing. The junction temperature is cooled by the transistor case which may be connected to a heat sink.
It is a common design principle to arrange the power supply voltage to sag under excessive load so as to prevent the junction temperature from exceeding safe limits, and thereby prevent the transistor from destruction if an unsafe drive level is applied.
General purpose amplifiers, such as might be used to drive passive loudspeakers, with unknown crossover impedance characteristics, require rather different design parameters to amplifiers specifically designed for use in an active speaker design. Damping factor alone might be just one such consideration.
BTW, AVI active speaker amps don't use a couple of simple transistors as output devices. They are designed around very special compound devices, with very high gain, capable of very high power, and with great efficiency (low heat). I assure you there is more inside the casing than might seem apparent at first sight, and that the speakers will go very loud indeed with no shortage of power. AVI's stated power handling statistics are representative of this fact, and give a good guide to the 'real world' performance. Ask any, of the now many, experienced AVI users for confirmation of this.
It's worth bearing in mind that music isn't an 'RMS' continous signal, and for true fidelity very high power is required for true signal handling if clipping and associated distortion is to be avoided. An 'RMS' test, or rating, is unlikely to be sufficient to represent musical performance under real conditions.
JC