You just run out of available level. Clipping has always been a dirty business in conventional transistor amps. In contrast, tube amps gracefully bow out of the sonic act rather than abruptly exit stage left via a hard clip. The result is an often more pleasant musical experience. The Millennium takes an ordinary pulse code modulated signal and turns it into a pulse width modulated data stream.
Regulation is achieved by varying the conduction time of the transistor switches.
The processor in the Millennium enables the Equibit algorithm to digitally select the correct pulse width combination from among 256 possible width choices. The analog waveform is output only after the optimal result is computationally determined. Notably, the Spectron is also a pulse width modulated amplifier but it uses an analog technique to control the pulse widths. TACT recommends using the Millennium with speakers that are reasonably sensitive. Any speaker with a rated sensitivity above 88 dB should produce good results.