It also raises the question as to whether the built-in headamp is internally fed from the balanced or unbalanced output?
People like to say that the balanced/unbalanced difference only boils down to a volume increase but most DAC chips output in balanced mode and require an additional buffering opamp stage in order to go unbalanced, so as usual the rabbit hole goes deeper 
A/B'ing both off the DP1 could turn out to be complicated due to that volume difference, but I would guess that an OPA627 buffering stage would color the sound quite a bit anyway. Balanced should only be PCM1795 > I/V stage.