" One thing to understand is that the USB interface, and in particular, the master clocks, is the MOST IMPORTANT thing in a USB digital computer audio system"
I believe that proper word instead of "master clocks" would be the "real life jitter". The master clock's jitter shows the potential, however, when you build your server or DAC (or buy elsewhere) number of factors will degrade its actual performance and it depends solely on the builder to isolate and "annihilate" them. Its not "off-shelf" stuff.
Also, I must mention output stage... for generations, most modifiers here made their living on upgarding output stages and every one with ears know the improvments of "better" output stage.