Amir's measurement of the improved SINAD at higher levels than 4 Volt output inspired me to show the superiority of the ADI-2 DAC's multiple hardware reference levels, that anyone can use without having to think about it by using the default AutoRef setting. What happens is that when you lower the volume every 6 dB (4 x ) the discrete hardware lowers its amplification and the DAC's digital level is ramped up again. So lowering the volume will not make you loose all the THD+N, or SINAD.
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First I replicated Amir's measurement (pretty much identical), then added the SINAD states that occur when the hardware level is changed. That didn't fit completely into the measurement, and also requires a logarithmic scale on the x axis for the lower levels. Then I set the reference to +19 dBu and schwuppdiwupp had the SINAD that one gets when changing the volume at the unit. Finally I added the ref levels in balanced and unbalanced mode on top as text. I hope this is understandable. Also please don't get confused: this is about manually setting volume digitally at the unit, not about a swept generator with automatic output level action - that would make no sense.
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So what it shows is that when you use a standard DAC and only look at the SINAD at 0 dBFS you miss it all. How often do you use 0 dB volume? Most of the time people lower the volume, definitely so when using phones. You can take the best DAC ever measured at ASR- it has no chance against the ADI-2 DAC at a real-world volume setting of (for example) -20 dB.