I am not sure if any of these amplifiers even have a digital input.
The thing that is totaly unfortunately misleading about class D amplifier is that they are always called "Digital" even the title of this thread, the title of the shootout etc are wrong. They are "switching amplifiers", not digital amplifiers, and they are completely analog from the input to the output.
I believe that there are a *few* amplifiers that have some sort of digital input to them, but even with SPDIF data there needs to be a conversion process to get to some PWM format etc, and some filtering or oversampling to prevent aliasing.
Add to that the fact that you have to control the volume somehow and you DO NOT want to do that by chopping bits, even when well-dithered, you start to loose dynamics at some point.
So, the bottom line is that none of these amplifiers could even accept a digital input without having a D/A device inside of them, and to perform this at line level and feed the analog signal to the analog input of the analog amplifier.
Now, one common argument is that the output stage is switching on and off, however, the time duration of the on/off cycles is infinitely adjustable, so it couldnt even be charecterized as a digital output. It would be an analog output with two states, pegged at the negative rail, or pegged to the positive rail, but with an infinitely variable duty cycle (time spent at one of the states vs. the other).
-Paul
