Hi there,
Late in the show here, but aren't class D and E just the cat's nose?
Class D mimics an analog signal by filtering a PWM signal (x-times oversampling equired for quality) though a low pass.
Class E generates a sine signal directly from a rectangular signal that equals the target frequency. Conversion between REC and SINE is done by a CCL filter at resonance.
In the core, yes, in both types convert a "digital" signal to a analog one by filtering.
20 watts! Did you try amplitude modulating it?
I set it to 20W. The shown board is capable of delivering 60W peak carrier from 12V. Likely more with other components. Class E is fairly easy to upscale. About modulation: yes, whatever can supply with with a positive-wing-only-signal works. Some classy monorail amp with the blocking cap on the output removed will do fine. Or some cheap Opamp-Stuff. Or, if you like to stick to "keeping it efficient": some PWM Amp.
Kind geetings,
Zazzle.