@hwfanatic
Yes I do, in the sense that the correct metric is unknown. Concrete example, most people here would swear that different coupling caps sound different. OK, we could measure something, say, dielectric loss, that might be perceptibly different for different capacitors, but we can't say for sure that this is what we should measure to properly evaluate which capacitors sound better. I could measure, at work, the dielectric sprectral response accurately from subHz to GHz, and surely each capacitor would look a little different. But again, I have no way of connecting that information, however detailed, with any differences I might hear.
I rely on measurement and testing for troubleshooting, confirming the basic operating points, and a kind of pass/fail minimum performance benchmark. Once it's clear the circuit is running to specification and is basically solid, the rest is done by listening evaluation.
@nereis
Because the Sapphire's diamond buffer is doubly-symmetrical, using the same transistors fro the driver and output, the DC offset, and DC stability is incredibly good. The total output offset is mostly from the op amp stage, the buffer itself contributes very little. Likewise the transients on turn on turn off are no worse than the op amp alone.
I don't think we need to play the personal preference card or invoke any quasi-religious philosohy. THD is a very crude metric of the level of distortion, it gives equal weight to all the distortion peaks, regardless of whether the harmonic is even or odd, high order or low. It's a time invariant measurement using a simple sine wave input signal.
By analogy, it's like judging how fast a car can go by measuring the diameter of the wheels. There are other, better measurements, but eventually each and every one runs into the same fundamental problem: you end up chasing the measurement rather than using it intelligently towards the end goal, which, since we are in the business of making great sounding audio equipment, should be clear to everyone present: better sound.