I use the X5 via coaxial.. I've run a coax line and USB line up to the console so I can run phone USB or Fiio SPDIF coax, either.
So the OEM head unit pretty much turns stuff on, that's about it.. However, I will play with it's outputs and see if I can get better at measuring the OEM electrical signals through the DSP out somehow to the Focusrite interface.. I think I need some sort of attenuator for that. So good excuse maybe to look into a DM-RTA audiocontrol piece. Sorry off topic.