One cannot simply swap out an AB amp for a D. The system must be coherent and matched.This seems to be in response to my post so I will bite...and ask what do you mean by "coherent and matched?"
I didn't mention that I tried the amps with three different preamp options, two of which were made specifically for the amplifiers, by the same manufacturer that made the amplifiers. Because two of the preamps have low impedance outputs, those two matched well with either amplifier wrt impedance. The highest gain preamp was +6dB and the other two have zero gain, while the source is 4V. These numbers work well with either of the two amplifiers. Are there other parameters that need matched? Regarding coherence, what attribute or parameter would make one preamp more "coherent" than another when used with a Class AB or Class D amp, and couldn't the same preamp be "matched and coherent" with both of those amplifiers?