One possible method is go back to BIOS and check if there are some other useless devices, disable and release them to give IRQ number to the cards.
But I personally suggest you install these cards to two different servers, so that you will be able to have the cards have their own IRQs. For a dual-core CPU, four cards simultaneously work in one machine would be not a good solution, especially there is single-port digital card.
The server would not be able to sustain so heavy workload.
