There is absolutely no way for speakers to be driven digitally. A speaker is an analog electro-mechanical device that expects an alternating current signal within its range to operate. Digital Os and 1s are on-off states in bitstreams that a speaker will never understand and will, in fact, be seen as square waves that, at sufficient current, will destroy speakers.
Hence, those digital amplifers may have no DACs along the audio path, preserving everything in the digital domain up to the very last end, but it has to synthesize or recover the analog waveforms from the digital square waves right at the amp output (these are essentially high gain high power DACs). So that speakers can understand and convert them to the proper accoustic energies.
Pure Digital amplifiers are almost revolutionary in their application, preserving what audiophiles hold dear in linear amps while achieving 90% power effiiciencies. They are said to be the wave of the future, putting class A and Class A/B amps on the same road that dinosaurs went through.
I am still learning about this new technology.
In addition to the Tripath class T amps mentioned in another thread, you may want to check this site:
http://www.spectronav.com/tech1.htm
