What are the minimum required pieces for checkmate in 3d chess? Assuming the rules of millennium 3d chess, what are the minimum required pieces for checkmate?

I realize this is an extremely difficult question, but in regular (2-dimensional) chess, we have rules of thumb for when two players should draw during the endgame.

A few examples of these kinds of scenarios (in 3d chess) would be much appreciated.
The following are minimum involving various pieces:

King + Queen
King + Rook + Any Piece
King + 2 Bishop
King + 2 Knight

This is only the theoretical minimum to actually mate. Whether or not it is possible to force a mate in this situation is a different question. You can see these mates by placing both kings in a corner, one on board 1, and the other on board 3.