My understanding is that a Class G amp will distort differently than other amp designs, and that historically, distortion and with Class G how it exhibits itself in regards to sound quality (always near and dear to audiophile types)has been problematic. One would expect that newer Class G implementations would have a handle on that at least to the extent of providing competitive sound quality though I am pressed to see how Class G alone would result in better sound quality than Class A/B. Perhaps, this is possible at a particular price point, but not categorically?
I suspect Class D is a totally different beast in regards to sound quality and how it distorts compared to Class A/B/G amps so I am not sure a comparison is even warranted there.
