Trifire setup - General Question

I have 11.1a catalyst drivers (11.1 won't install on my crossfire setup, though it works just fine on my single card setup).

I just added another 5850 to my setup. So I now have 3 5850s on an X58A-UD3R motherboard.

When I go to the crossfire settings in the AMD catalyst software, it gives me the option to use '2 GPUs (6 9)' for crossfire or '3 GPUs (6 9 4)' for crossfire.

What do the numbers (6 9 4) mean? Are they channels of some type? IRQs? DMA channels?

Thanks to anyone providing the answer.