The XMOS demo board sold for $149 in digikey. The firmware need to be loaded before the board can be used. There is a digital out from the USB 2.0 demo board and thus it will be a easy interface from USB to FDA-1 optical input. What you need to do is to get an optical cable to link up output of demo board and input of FDA-1 Toslink. I have tested this mode and the sound is better than using Ti PCM2707 USB receiver with I2S output.
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On board, there is a I2S connector and thus the clock jitter measurement is taken at the MCLK, BCLK, LRCLK locations. The jitter at MCLK from 48k to 192k Fs is from 10 to 13 pico second respectively which are excellent. In fact the MCLK is taken directly from the onboard crystal oscillator after the buffer logic IC. For jitter at other clock like BCLK (Bit Clock) and LRCLK (Word Clock, Fs), they are as high as 800 pS or above. For any DAC using the MCLK as the clocking reference (like FDA-1), the result should be very good.
Attached is the document of jitter measurement for reference:
Jitter measurement by Lecroy DDA-120
From all the measurement, the lowest jitter mode is to set the output of the USB 2.0 at 24 bit with 48k Fs.
With a more accurate period jitter machine Wavecrest DTS-2070C, the jitter at MCLK is measured at only 4.6ps. See attached document:
Jitter measurement by Wavecrest DTS-2070C