In order to make broad conclusions about USB IMO, they must have auditioned every USB interface with every server configuration. This is highly unlikely. They can only rely on their own experience, just like the rest of us.
There are a lot of poorly conceived USB interfaces, even big names. Most of them on popular DACs are not that great. This is the reason why some people have a less than stellar experience with USB.
If you ask Antipodes, whose server is excellent, they would likely make the opposite claim, that with the RIGHT USB interface, USB is far superior to S/PDIF.
I, on the other hand have had a LOT of experience with many different high-end PCI cards, Sonos, Squeezebox2, 3, Duet, Touch, Firewire interfaces and several USB interfaces, adaptive and Async. I have designed or modded all of the above. My USB interface is 5th generation (Off-Ramp 5) and 6th is in prototype stage. I have used or modded servers including Naim, Qsonix, Soolos and Antipodes as well as modified Macs and PCs. I believe I am in a better position to determine which technology is superior. Empirical Audio has been in business for 18 years and I have been doing digital design for 38 years. Async USB driving S/PDIF or I2S can be every bit as good if not better than PCI bus driving S/PDIF, providing a good design and implementation. Driving I2S it should be better because it avoids S/PDIF conversions.
Steve N.
Empirical Audio