Hi kcarlile,
OK, get ready: these things are complicated. You are correct that class D does not stand for "Digital", although through frequent usage, it has taken root.
Class D amplifiers, although there are a number of different design variations, are essentially switching amplifiers or Pulse Width Modulator (PWM) designs. B&O's "ICE" modules are also switching designs.
The incoming analog audio signal is used to modulate a very high frequency PWM carrier that works the output stage either fully on or off. This ultra-high frequency carrier must be removed from the audio output with a reconstruction filter so that no ultra-high frequency switching components remain to corrupt the audio signals. Class D designs are extremely efficient, typically in the range of 85% to 90% or more. Axiom's A1400-8 reaches 95% efficiency at full output. Conventional class A/B transistor amps' efficiency is about 50% to 60%. The unused energy is dissipated as heat.
Regards,
Alan
