Here is a link to a very interesting kit based on a renowed DAC (AKM AK4399): http://www.audiophonics.fr/en/kits-modules-diy-dac/dac-akm4399-i2s-vers-analogique-24bit192khz-p-8963.html
However, there is no internal clock on this kit, and as the RPi does not generate clock on I²S, it would not work out of the box.
This brings a question to my mind, as explained on this web site, I²S is the best possible solution for an audiophile DAC as the clock is synchronous, I fully agree with this assertion. But as the RPi does not generate the I²S clock, the main benefit of I²S seems to be lost, or in other words, what is the difference between I²S without clock and USB, as both require an external clock generation?
Forgive me if I am wrong, my knowledge of digital audio is limited, but I would really appreciate if someone could explain me this.
And, of course, if anyone has an idea on how to generate the clock for this DAC kit, it would be really appreciated.