Yea, that was not the best example but example nonetheless. My intention was to show that most opamps, which are often the heart of most headphone amps, distort when driving capacitive loads, the difference is presented in % of overshoot. Square wave is just a way to clearly show this overshoot, and while opa227 is not the most vulnerable opamp in this respect it does show some differences. Now, even though we know that there is some difference since we measured it, as we all hear differently, it can not be said that if something is measured to have x or y of something then it is audible. Some poeple have bat-ears and some have impaired hearing, some use equipment that is poorly designed and distorts heavily when presented with even small amounts of x or y, and finally some use well designed equipment that is not very cable reliant. This is what I meant by writing that it's subjective.