It was somewhere outside Barstow when "TheNewGuy"
wrote:

Can I put a purely cupped board in and get to two flat, parallel faces?

Yes - but:

Don't try to take too much off at once. This increases the pressure
from the feed rollers and bends the board as it goes through - so it
emerges still with a cupped face.

It's not quick. It's usually quicker to knock off the worst of the
high spots with a hand-held powered planer beforehand (the only thing
I use one for)

You should try and even the board up before feeding it - lower the
high spots on each side, so that the board is level. If you feed it
through so that teh bulk of the timber is tilted, then you have to
remove even more stock before getting a useful board.

As for any board, bad cupping requires a lot of waste to be removed
before obtaining a flat board. It may be more efficient to rip it in
half first, providing two narrow, but thicker, boards.

Bad cupping usually represents a lot of stress in a board. Expect the
board to warp further as you remove this stress - take it halfway
down, leave it overnight, then go back to it.

You'll have a lot of trouble planing a warped and twisted board. Think
about cutting it smaller instead, or even putting it on the firewood
pile.