Julian,

For red book CD resolution you would need a bitstream ADC with sampling rate equivalent to 65536 (2^16) pulses for every 44.1kHz sample. Digital amps don't have sampling rates of 2.89 GHz (65536 x 44100). That way, you are loosing precious resolution...

It's like upsampling but, this time, to a much higher sampling rate, say 500 - 1000kHz... the (analog converted) 16bit/44.1kHz digital data from the CD player is then re-converted in the amp by interpolating new samples...

Would you like the sound of a 2.89 GHz switching amp better?