> please correct me if I am wrong ...
Well, not knowing the Nbox's circuitry, my only quibble would be that this isn't a phantom powering arrangement of any kind. The 60 Volts is the capsule's polarization voltage. It is simply sent along on a wire all its own in the cable, without going through the whole Wheatstone Bridge rigamarole.
It's almost like with tube microphones, where the plate voltage was sent from the power supply to the microphone along one wire in the cable, the filament voltage on another, and the audio came back along totally separate leads with no DC on them. Generally the capsule's polarization voltage (which requires almost no current once the initial charge is established) was taken from the plate voltage, except in microphones with remote-controlled directional patterns.
The only differences here are that (a) there's no vacuum tube (that I'm aware of) in a Colette cable or an Nbox; (b) the two DC voltages are for the capsule and the FET in the head end of the Colette cable; and (c) the audio signal is unbalanced, so it flows in only one conductor and is measured relative to the shield/ground.
--best regards