Wavelength WaveLink Asynchronous USB to S/PDIF converter.

Nice, seems to be a great summary of the issues. It is somewhat surprising you dont see more slaved PCI transports, as it really doesnt take much to implement, and some even can be made to sync to an input signal, so would require no hacking.

Colin, I've played with slaved PCI soundcards. First they require a wordclock, so there is a quality loss in that conversion from your DAC master clock, then inside the PCI card a PLL synthesizer converts the clock to a freq compatible with the card (more degredation.) In the end the quality was not worth it to my ears.

The Asynch USB transports are the way to go, hopefully someone will offer the Ayre implementation standalone so DIY DAC builders/modders can eliminate the SPDIF and have galvanic isolation.