I have built an audio amplifier with a Texas Instruments LM4766 chip amp. It works beautifully. I have performed some torture testing that involved driving a pair of large bass cabinets (rated at 300W), mostly to determine if my proposed heatsink is sufficient.
When I drove the amp as loud as it would go before audible clipping, I noted the maximum temperature of the heatsink tab after it plateaued (59C). Then I pushed it into audible clipping, and the temperature of the heatsink tab dropped to about 56C. In an attempt to keep it somewhat scientific, I used the same audio content for the range of testing.
The question then is this; when the output devices clip, are they entering saturation mode and turning fully on, thereby dissipating less heat? Could it be so simple?