I would say it's what important in the sound to you, a particular listener, that determines the value of conventional measurement. I was at a demonstration of the DEQX unit, years ago, done by one of the key people in the company - they're developed in Sydney. And found it remarkably uninspiring - yes, before, a very wobbly FR, after, straight as a die - but the subjective quality of what I was hearing hadn't changed - it was still just reasonable audio sound, nothing to get excited about.
More recently, I spent a number of listening sessions with a local enthusiast who has really gone hard on the sound calibration adventure - he's had the DEQX people in his home, and was pushing them hard to "get it right". Fully active setup, using Scanspeak drivers, and big Naim amps - at its best it was very, very good, but I didn't hear specialness from a dead flat FR. We tried a frequency sweep from a test CD, from bottom to top and down again, etc - very consistent, almost perfectly clean sound.
Interestingly, most of the subjective quality issues seemed to originate in the DEQX unit itself - from cold it didn't perform well, it needed an hour or so to come on song. The owner was not happy with the raw quality when he first got it, did major internal surgery on it, managed to kill it(!), got that sorted
- and throughout has been talking to the DEQX people a lot, prodding them to improve things ...