Isn’t the NPX300 classified as a suitable for digital sources - which the NSC222 effectively is. So has an output for analogue and an output for digital circuits. A pre would, I assume (hah!) just require a supply for analogue circuits, which is what the Solstice PSU provides?
[edit: I think the “Type 3” and “Type 4” terminology might start to make more sense with the release of future components? Plus this post:
Only the one burndy connector on the Solstice PSU, plus a DIN8
]