What do you mean? Class D amps are essentially PWM driven amplifiers. Essentially any speaker in existence offers enough low pass filtering to be directly wired to the amplifier, as well.
Generally they use pulse density modulation, rather than pulse width modulation, which increases the frequency of the noise and makes it easier to filter out. Sigma delta modulation, which the comment you replied to mentioned, is a way of doing pulse density modulation.
Imagine if you did dithering to produce grayscale images with a black and white screen by just using different sizes of rectangles; you'd have to have a very high resolution screen before you wouldn't be able to see the individual rectangles. That's what pulse width modulation is like. Whereas pulse density modulation, using a sigma-delta modulator, is more like a proper dithering algorithm, where you spread the pixels out evenly across space, you don't just use different size rectangles to represent different shades of gray.
Also, there's a world of difference between PWM out of a CPU running a non realtime multitasking OS with continuous scheduling and varying timings and the same PWM produced by a dedicated chip that does nothing else.
