erik - This is probably not the place for this discussion, but here goes anyway. You have to understand that the DAC completely reclocks the signal using its own internal clock. The DAC receives the data from its usb input, puts the data into an internal buffer and then pulls the information from its internal buffer and, using its internal clock, reclocks the signal. That was done by Brystron to avoid jitter problems on the USB.
Please explain how the sync timing on the USB effects the internal reclocking of the signal. The only way it can is if the sync usb cannot fill the buffer fast enough, which is very unlikely.
The reclocking process is not done by all DACs. Many just use the timing that comes through the USB, in which case async is certainly preferable to sync USB. But, since the Bryston DAC uses its internal clock to reclock the signal, the jitter on the usb does not make its way into the final data.
You might want to read the Stereophile review, in which they clearly state that the BDA-1 reclocks the signal internally, in order to control jitter.
http://www.stereophile.com/digitalprocessors/bryston_bda-1_da_converter/From the review
"
One of Bryston's primary goals for the BDA-1 was to reduce clock jitter,
ie,
mistimings of the digital datastream presented to the DAC. Unlike the
company's BCD-1 CD player, a one-box transport and DAC, the standalone
BDA-1 must reclock all signals fed to its data inputs"
As an aside, I used to make my living doing realtime programming on realtime operating systems. The issue of timing incoming signals coming into a computer is well known to me.
