I have to apologize,
repost from tweekgeeks hiface faq
28) Does the hiFace work in asynchronous mode?
Sure, the transfer of data over the USB bus happens in a totally asynchronous fashion, with respect to their retransmission to the DAC, in short packets which use all the available bus bandwidth. Actually, hiFace is master in the transmission from PC to interface. As it uses its low jitter oscillators to time the S/PDIF transmission, line jitter is totally uncorrelated to data transmission from PC to interface
repost from tweekgeeks hiface faq
28) Does the hiFace work in asynchronous mode?
Sure, the transfer of data over the USB bus happens in a totally asynchronous fashion, with respect to their retransmission to the DAC, in short packets which use all the available bus bandwidth. Actually, hiFace is master in the transmission from PC to interface. As it uses its low jitter oscillators to time the S/PDIF transmission, line jitter is totally uncorrelated to data transmission from PC to interface