Normally Linear amplifiers lose a lot of power into heat.
What are the possibilities of using a switching FET output to recreate the apparent audio signal?
Say, run the switching PWM FET @ around 48Khz and create an LCR crossover which act as a low pass pi filter to reproduce the apparent linear audio waveform to drive the speaker coils?
CDs rebuild audio from PCM already at 44.1Khz data encoding.
Yes, it's been done many times. You can buy audio power ICs that use Class D (switching) outputs to get high efficiency. They're often used in battery powered audio amplifiers to maximize battery life.
Texas Instruments have a few excellent class-D audio power amplifier ICs. They switch at a very high frequency so that the output filter works well.
They are so efficient that a fairly high output power requires no heatsink on the IC.