Amplifiers can produce huge amounts of power, much more than many individuals think can be achieved when sourced off a typical 20 amp, 120 volt circuit. Due to stored capacitance, and the brief duration of transient peaks involved in the source material, amplifiers can exceed the limitations that Ohm's Law seemingly presents.
For starters, a circuit, for this purpose a 20amp/120volt dedicated residential circuit, can pass huge amounts of current as demanded by the connected load. The reason for this is to avoid nuisance tripping for items such as motor loads. Loads such as these may require several times their normal rated draw for periods of start up etc. So it's not uncommon to see a motor load, such as a refrigerator pull 20-40, up to 80 amps momentarily during start up. The circuit breaker, by design, allows these high currents to pass to avoid nuisance tripping.
Oftentimes typical breakers may allow amounts up to 7x their rated amount, to pass for about 1.5 seconds. At that point the tolerance for the allowable current begins drop and tapers toward 2x rated amount at about 30 seconds. So for the initial 1-2 seconds, up to 140 amps is allowed to pass in our 20 amp circuit example. Then subsequent extended periods can draw as much as 40 amps for as long as 30 seconds or so. This is a huge amount of current, and quite significant to our discussion.
So we now know the wall circuit is up to it, so it all depends on the robust nature of the amplifier design. First the power supply, and the output stage determine peak power capability, and continuous output capability. Generally, as we're well aware, nearly all source material we encounter that's associated with either music or film releases, possesses transients that vary in length, but generally they are quite brief in the larger scheme of things.
Amplifier mfrs. quote RMS, however this doesn't necessarily mean continuous. This merely means the amp can produce that much power for some generally undefined period of time. Some mfrs. may cite the exact amount/conditions etc., but the marketing department intervenes and perhaps embellishments ensue. The question is how long it can be sustained, and really how long is actually needed. Unless one is pumping out very high average levels, which isn't that common, the real needs are quite brief.
We need amplifiers with enormous peak capability, that we know. System wide, we can build in enormous system peak capability through multiple amps/drivers covering the all important LF range.
But, back to your question; mfrs. can build amps that can produce 6000 watts from a typical residential circuit. The circuit's good for it. And via capacitors and either a trick, switch mode power supply, or an old school over built jumbo transformer and huge amounts of capacitance power supply, we can get amps that can track a signal and produce brief amounts of several thousands of watts.