I'm not saying there aren't other important characteristics of a DAP (THD+N, timing/phase, IMD, RFI, etc.), but FR is the be all and end all if we're talking about brightness of a sound signature. A FR sweep would trigger harmonics in the exact same way if the final output was to your ears rather than to the sound card. I suspect a large part of any perceived differences in FR are attributable to 1) change in headphone FR with changing z-out 2) reviewer necessity - what else are we going to write about in our reviews if they all sound the same? As you say, we're probably getting OT and boring most other people on this thread, so I'll drop it here and maybe we can continue via pm?