@lanx0003 You're misunderstanding me. I2S is the native digital pathway in every dac, this is the DEFAULT clock used regardless of input chosen. Section 4.2 simply states one can sync or use DDC I2S clock OR use dac internal clock using async. Important point is local clock is in FACT a I2S clock, it is the native pathway in every dac, this just a matter of semantics.
And these are NOT unique features of udac and Harmony. Many dacs with I2S input and DDC offer sync or async options, as well as configurable pin.