Wish granted, Les. Here is Kingwa's response:
I think this test is by RCA output.
We always design RCA output has a little warm than XLR and CAST, so RCA output is a little roll off than XLR, but you can ask some one to test most wellknow oversea brand CDP or DAC, years ago I ever test Marantz ,Accuphase, Marklevinsion ect CDP and DAC, they also roll off a little.
I accurate remember Marantz CD7 (because it was my love), it roll off -2DB at 20KHZ.
Why most CDP or DAC will roll off?
PCM data has a lot high frequency noise, so oversampling DAC apply the digital filter to attenuation these noise , but after digital filter, feed to D/A chip, the DA chips also bring the new noise, so the normal DAC must design a 1nd to 4nd analogy filter after the DA chips, the analogy filter usually roll off -3DB at 25KHz to 44KHz , and let the brand under 20KHz has a little roll off.
If the DAC is NOS, the roll off is much more than OS DAC, usuall at 20KHz has -6 to -10 DB roll off.
If the DAC/CDP don't design the analogy filter, the high frequency easy make not roll off at 20KHz, but the problems is the noise no attenuation, and feeb to the amp, the noise will effect the signal and let the amp born a lot distortion, though high frequency is not roll off but sound much bad.
I ever buy a lot oversea CDP and DAC for study at some years ago, they all have the analogy filter and let the hign frequency less or much roll off, this is normal, but I also see some bad grade CDP or DAC not roll off indeed boost up the high frequency, these not they have good technology, the reason is the output amp has oscillate.
Upon is base of normal analogy technology, but if apply CAST technology and CAST output, there is much excellent than normal analogy technology, so I think CAST is much neutral than normal output, and said XLR only has 85% of CAST in the combo.
And I want to say, human ears much different to test meter , zero distortion, very wide brand, the test meter will tell you this is a excellent gears. But if listen to these gears, you maybe not gree with the test instrument. Just like Tube gears, they has unacceptable distortion and noise, but why a lot fans love listen to tube gears?
A lot student if finished electronical university course, they maybe can design and make a amp has very excellent test parameter, but do you think they all can make the good gears for listen music?
There are a lot audio brand in world, because there are most fans will enjoy different music style, some will love warm or tube like , some will love dynamic, some will love neutral. But what is neutral? I think there are a lot manufacturer affirm there gears is neutral. this depen on the designer experience , not depend on the test meter.
If depen on the test meter, I think all gears in world only has one sound style. Just like the copy humans in << Star War>>.
Finally, I think you can ask some one to test some other well know brand CDP/DAC like Krell or Wadia or other well know brand, then you can understand what happen.
BTW, we can make the DAC output no roll off,(cancel the analogy filter only), but I don't think this will has better sound level.