Subjective perception of bass involves not only involves measurements of the lows, but also measurements throughout. Few bass instruments or sounds, even electronic generated ones, exist solely in the low frequencies. It's the higher frequencies, the harmonics which make up the whole. In addition, tools to help us understand the sound include distortion and the attack and decay envelope of bursts (including ones outside of the frequency range being discussed). Note that my distortion measurements are radically different from those of RTings and RTings does not provide transient response type measurements. The deeper extension of the HD560 S and flat midbass in respect to HD6xx series was shown by my own measurements (post #2)*. If this is what you mean by accuracy, then the HD 560 S is indeed more accurate. However, frequency response is only one piece of the puzzle that explains sound. If we combine several measurements FR, distortion, transient response, decay - we perhaps get a better picture - but it still does not fully explain the sound. Note that I did not say more accurate. I simply said "didn't sound quite right". My guess is higher distortion on the HD560 S in the upper bass, a slight frequency response dip in the lower mids, and a slow attack rise for the 50Hz burst set - maybe the limp dick attack burst at 4kHz and elevated treble FR just past that. *Did you look at any of the measurements and related discussion here, or did you gloss over them only to reference results on RTings? Because going off the measurements here, the HD560 does have more accurate frequency response than HD6xx series as well.