Aside from a wide range of parts to choose from, there are other engineering trade-offs, such as the filter on the CLass D amp for EMI/EMC and the noise on the power supply rails.
This, of course, is even before deciding on a speaker.
Is there a standard method for an objective and repeatable evaluation process? If so, what sort of equipment and methods do I need, and what metrics do I need to calculate, and how to these metrics relate to the perception of audio quality?
(Second note: This isn't an evaluation of codecs, compression, sampling or other DSP artefacts. I have control of the bitstream I send to the audio codec chip. Advice of choosing the signal I should send is most welcome).