The rDAC is one of the few that allows better than CD quality over USB.
But to get this, you need a third party driver. Which is currently only available for Windows. With the built-in sound drivers in Windows or Mac, you'll only get 16 bits/48 kHz (= CD quality) over USB.
I have seen this mentioned in the comments section of the review, has anyone tried this or is it benificial, many thanks in advance.