CM, the key word omitted in your quote is "fractionally". But the real question is what the heck does "ultrasonic attenuation" mean?
according to the web..."
Ultrasonic attenuation is the decay rate of the wave as it propagates through material..."
It's hard to imagine a listener could discern fractional differences in decay rate. Must have really good ears! Nonetheless, the list of pros is quite impressive and greatly outweighs the cons

Nice going Bryston! Congrats on all the great reviews

TJ