Unless someone proves that human hearing can exceed 20kHz, I believe any reporting on abilities above the threshold of hearing is somewhat superfluous (only somewhat, I still enjoy seeing the measured differences), especially harmonic distortion, which will be multiples of the fundamental, but rising in frequency. I've had a number of amps, and respected DACs, and though I don't currently use the output of my MB (Asus Hero IX), which uses a version of the ALC1150, the 1220, the outputs were audibly silent when I did. The sound was very good, perhaps dry (or perceived as such due to low distortion?), but imaging was excellent and timbre was quite surprising. I literally took the outputs of that MB into a Parasound A23, then into a pair of Dyn Emit 10s, and it was a fantastic office system.
However, the headphone output on this MB uses a slightly different path. They brag about a dedicated headphone circuit, TI 4850 Op Amps, etc., but I've never gone back to use it. I'd expect a similar experience though, given the 300ohm impedance of those cans.