Jacques, you must be using a flash for all these shots.
Can you tell us how you use it, because it seems as if you are not using, and that is what we would like to learn.
Most of the 3Dx pictures in interior are with the SB 900. The flash is on TTl-BL, and the white card is fully extended while the flash head is turned toward the ceiling (or the sky, as what counts is the reflexion on the card). While I know I shouldn't, I'm often in Auto-ISO mode on the camera, so sometimes I have surprises !
Flash wise, it's just as simple as that... :-) Apart that with a D3x, a SB 900 and a 105mm f/2.8 VR, I feel like Weegee and his flash bulbs on his Speed Graphic camera...
With the Df I don't use the flash (I haven't yet taken out the small plastic protection of the flash shoe :-) ) and everything is much lighter !