If you believe in measurements then you know they are both transparent devices which means no audible differences can be heard. An APx555 exceeds the sensitivity of your ears like the Hubble Space Telescope surpasses the ability of your eyes. If you've proved there's some differences you can hear but can't be measured by lab instruments then it's gonna be an important scientific achievement that in fact most people here will want it to be true so audio can finally be a big deal, again.Of course, the choice of DAC is always based on measurements! not the ears, but as a result the differences can be heard and not small.