Typical of Japanese designed electronics of the era, they sounded a little "bright" compared to the US or European designs. If you threw them on the bench the IM distortion was a little higher. While I have no metric for this, you can watch the residual distortion trace on the scope and predict which units will seem a little bright (or raspy -- if you don't like it) The distortion trace will tend to be a little jagged on the bright units. This is a qualitative judgement, I have no hard science for this, but others have made this observation too, and it is not 100% predictive.