What is your understanding of "enable proprietary drivers"? If to register in a config it is not surprising. Because you have by default enabled the integrated card, that is logical, with drivers from NVIDIA will not work. Also worth noting that modern Xorg smart enough to palm off the correct driver.
Ubuntu, by itself, does cards does not react, for he sees only the default Intel (NVIDIA simply disabled).
Now more to the point: you ought to pick in the direction of vgaswitcheroo, though I do not know what is the situation with the cards of NVIDIA.