I am not an audio engineer, so don't take me as a reference, but what I know is:
When the amp shows 0 db, it is operating at its rated power and is
producing the amplification it was designed to produce. When you turn
the volume down it "cuts" the amplification and requires less power to
run and produces less heat. Conversly, when you turn the volume up it
"boosts" the amplification and requires more power and produces more
Somewhere I read that every 3 dB of gain or cut in amplification
incereases/decreases the power requirement by 2 times. So, if what I
read were true and if my interpretations are correct, when your amp is
operating at -3 dB, it is using half the power it was designed for. At
-6 dB one fourth. Conversely, at +3 dB, it is using double the power
and at -6 dB four times.
So, can that really happen? Can the amp really amplify beyond what
is was designed for? yes, it can, as Music is not one tone or one
loudness. It doesn't require a certain amount of power continuously. So
the amp does that "extra" duty when needed. But that doesn't come free.
When amp goes beyond its limits, distortion increases.
So the bottom line is: when your amp shows -xx dB, it will produce
best sound it can. When it shows +xx dB, its over working, its about
the time you get a higher power amp or a more sensitive speaker.