How to implement 5 SPI-4.2 inteface in Stratix-4

I need to implement my design in S-4 or S-3 which contains 5 SPI-4.2 interface. From the handbook, I noticed that only 4 SPI-4.2 interfaces are supported.

I am wondering what the limitation is. Is this limited by the number of DPA blocks or High Speed LVDS IO?