Maximum output voltage that a amplifier can achieve would be equal to the input voltage. But still i don't think that an amplifier can come into that state. So Now if the input voltage is V then the theoretical maximum power that an amplifier can go is


V^2 / R where R is the speaker impedance

Now if an amplifier is said to produce 2000Watt's, 1000Watt's per channel, at 48V AC then its overstated power am i correct.

 

Provided that it does not have a voltage step up switching circuit

 

A bridge amplifier can effectively double the supply voltage.

If the net total impedance of each speaker was 2 Ohms, then it could be do-able.

 

Crown has been using a "grounded bridge" power supply for years.
It effectively doubles the available voltage from the mains.
If you are interested, read this paper from Crown to understand the concept.
Link:http://www.crownaudio.com/pdf/amps/grbgpapr.pdf