Well, I think youve heard of what people had to do many years ago with riser cards.
Back in the early 90's when 3D graphics were just appearing, 2D and 3D were not combined on the same card. 3D had the main card, while there was a 2D "riser" card that sat above the 3D card.
In the present, graphics cards have integrated 2D and 3D functions. No combining cards can be done anymore.