and that’s the crux right there…..250, tube, ss, Class D or whatever is still the same power into a speaker. traditionally, audio power measurements were/are done into a resistor (2, 4, 8, 16 or whatever amount of Ohm) which is not truly representative of how a speaker really behaves. for example, a 4 Ohm speaker may go up to over 20 Ohm at higher frequencies making the “pure resistor” test/characterization method lack in real world terms. the reason the Audio Engineering Society (AES) chose this way is because it’s quiet and cheap (no need for audio chanbers to test purely electrical performance of the amp), and gives you unbiased amp data.
now, you add speakers and those earlier measurements remain purely a benchmark reference that doesn’t really tell you much about how the particular amp/speaker combo will perform…..add to that the variable of the signal (type of instrument for example) to be used and the complexity just keep growing…..
magnetic materials have come a long way and the recent NEO type magnets, although making everything MUCH lighter and portable are also MUCH more inefficient necessitating substantially more power to attain the same Sound Pressure Levels (SPl) adding to the confusion…..now 800 Watts is commonplace but you have to be very careful when you use an amp like this with traditional non NEO speakers or you’ll quickly fry them……apologies for the verbosity, the issues can become pretty involved…..