Just keep in mind that the doors that need X amount of cubes go by your total sum of both types of cube, so you can get in the 32-cube door with something like 22 regular cubes and 10 anti-cubes.
Nothing showing up like no image preview of the room? I think that just happens when you haven't been through that particular door yet, so if you can't find the door anywhere, it must be hidden. If they're the doors I'm thinking of, you need to do something somewhere to make them them accessible (I can't remember for sure if it can only be done in New Game+, but I know that's when I did it).