Brenn
It truly does depend on the how the equipment was designed, and what the focus of the unit was.....which inputs did they put their focus on.
In general I would always use I2S if that is an option, AES/EBU, then USB, then SPDIF
Balanced vs Unbalanced Digital Cables
I have the ability to go to a balanced digital from my Lumin d1 to my SMSL D400EX. Is it worth the potential expense?