I am wondering, are there any reasons to consider the ADI-2 Pro FS over this unit? I got offered a very good deal on a demo unit, but as far as I can tell the differences are the AD capabilities which do not concern me, and potentially double the output in balanced mode (do any headphones really need more than 1.5W of output?).
If you don't need the ADC then it's probably best to go with the DAC instead of the Pro.
There are only a few headphones which can make user of more power than the DAC has single ended.