So far as I know, with the DAC+ PRO the Pi I2S output is slaved to the high quality clocks on the HAT. If all else is equal, it is going to be superior to the versions which rely on a synthesized clock frequency generated by the Pi.
The problem is that, even if you start with a bit-perfect output, all else is rarely equal. I doubt if a good asynchronous DAC with its own high quality clock source would actually sound worse, provided the difference in the clock frequencies did not cause too many dropped or repeated samples.
