USB Async chip?

[boeserbaer]

Is there such a thing as a supported (ie good audio drivers exist for OSX and windows) USB chip which acts as a FIFO and you provide an external clock (same rate or serial bit rate multiple as your DAC)?

usb ==> [ magic chip ]
[ ]
extclk ==> [ ]
[ ] ==> DATA out to DAC
I don't really understand SPDIF, but it looks like when the traditional USB implementations connect to the dac via spdif, running async data to the reciever ic which syncs to the data and creates its own dac clock from the spdif stream. it seams to me that creating a quality dac clock to drive both the dac and to read out the usb chips fifo would allow the usb protocol to keep its fifo full regardless of the dac clock frequency, whereas the spdif data relies on the usb chip pll to read out its fifo, and if one were to use another clock for the dac, then spdif data would eventually either over or under -run. I suppose a smart person could create quality external dac clock, and run it into a pll to create the clock required by the usb part, and ultimately, the dac clock would match the spdif data.

This is the start for me of jumping into DIY audio, I want to create my own usb dac. I am used to designing for very low noise (<10 e- CCD ADC systems), and higher speed adc circuits 65Msps to 1Gsps.

Cheers,

Mike