"Power hungry" speakers

Hi folks, can you please explain to me why certain speakers so demanding with regard to amplifier power? I'm not talking about some notoriously-difficult-to-drive Apogees or some old Thiel models, but about speakers like the Sonus Faber Extrema's. These speakers do not belong to the realm of the less-than-1-Ohm-impedance-drop speakers, but need high powered amplifiers if you want to make them sing. Even 300 Watts wouldn't be enough! What is this for some ridiculous statement (or is this a fact?). What is the explanation for this phenomenon? I do not know much about physics, but I wonder what is happening with those Watts inside the speakers: will they be converted into warmth or something?