Right, for some academic purposes, for instance, a study on bats' hearing.
I agree that if you compare the CS43131 to the ES9219, then the latter is a better SoC. But I wonder why there are greater variations in THD performance (not including noise) of ES9219-based DACs whereas most CS431xx-based DACs perform very similarly. What would be the primary design factor in harmonic distortion performance of ES9219-based DACs? Your Neutron HiFi v1 has the lowest harmonic distortions I've seen among the DACs adopting ES9219.
That is, we are comparing this:
To this:
From a measurement point of view, this is a huge difference.
EDIT. By the way I recently measured both revisions of the Qudelix 5K with ES9218P and ES9219C. They measured the same and matched Amir's results.