It is adaptive USB not asynchronous. However audibly there was no difference when compared to the one that has asynchronous USB.
There is no SPDIF input possible as of now. All these questions have be answered on the designers blog.
This is how stereophile lauds asynchronous USB "To achieve the maximum resolution, a D/A converter must use a high-precision clock circuit running at a fixed frequency to control the timing of the conversion of each digital sample to an analog voltage. By contrast, almost all USB DACs operate in what's called adaptive USB mode, which means having to use a variable-frequency clock rather than a fixed-frequency master clock. For various reasons, a computer cannot maintain perfect timing of the data packets it sends a DAC via USB. Most adaptive USB DACs are based on one of Burr-Brown's PCM270x family of chips. The BB chip typically changes the master-clock frequency to match the average sampling frequency of the data it receiveshence the "adaptive." The drawback to this, says Ayre (and which John Atkinson's measurements of other USB DACs seem to confirm), is that adaptive USB DACs tend to have high levels of jitter. Also, the BB receiver chip maxes out at a resolution of 16 bits and a 48kHz sample rate."
However, the main benifit from the same is low jitter which the ODAC has even on adaptive USB. here is the evidence:
"NEW JITTER FINDINGS: I did quite a bit more research on jitter during the ODACs development. Im also using a new dScope method that shows the same spectrum as before but now the symmetrical jitter components are marked (with a white X) and summed to obtain a total numerical value (previously the dScope was just showing the total residual noise floor). Having the single number (-103.3 dB below) made it easier to optimize the ODAC for the lowest jitter. The objective evidence conservatively indicates if you keep all related components below -110 dB, and the total below -100 dB, the jitter will be entirely inaudible. Jitter creates dissonant distortion products in the audible band. Its reasonable to assume if the audible effects of jitter are kept at or below the inaudible noise floor, they too will be inaudible. So the same levels of 100 dB and 110 dB that apply to noise also apply to jitter contributions. This is also consistent with various professional reviewers and their anecdotal opinions on jitter performance as well as my blind testing against the Benchmark DAC1 which has even lower jitter.
ODAC JITTER: The ODAC passes the conservative criteria with several dB to spare even on the worst-case J-Test signal. And the spread at the base of the signal (very low frequency jitter) is extremely minimal being entirely below 130 dB. Its also worth noting the jitter here looks subjectively worse because the noise floor is much lower than most of my jitter measurements which are done with a 16 bit test signal. A 16 bit noise floors masks most of the spikes seen below. The ODAC also has negligible inter-channel phase error and essentially perfect pitch accuracy:"
http://lh6.ggpht.com/-zJ0sM8XXilI/T...202%2520Vrms%252024-44%2520ref%255B5%255D.png
