To quote the Stereophile reviewer:
"...the output above 15kHz dropped significantly, to –3dB at 20kHz. This kind of response is not that audible in itself. However, I am becoming convinced that the better time-domain performance offered by the digital filter that produces this response does sound better, particularly regarding accuracy of stereo imaging."
So he's saying that the (digital) filter that is responsible for this poorer magnitude response offers better phase (time-domain) response.
I would definitely agree with him on that point. If you want to improve phase response (time delay) you can give a little on magnitude response.
