Asus P5Q Pro & Adaptec 5805 Raid Controller

Hello,

I have a Asus P5Q Pro Mainboard and want to extend my system with a Adaptec 5805 RAID Controller. My board has 2 PCIe x16 slots and the RAID controller will need a PCIe x8 slot. My graphic card is a Sapphire X1950Pro which is in one of the 2 x16 slots. I know, that the board will slow down the both x16 slots to 8 lanes in CrossFire mode. I've no problem when the relativly weak X1950 runs only with 8 lanes. The question is: will the RAID Controller work in the 2nd x16 slot (with 8 lanes) or are both slots for graphic cards only?
This diagram of the P45 says, that both are for graphics. I'm really unsure because i thought, PCIe is for every device.

Please help because i don't want to buy this expensive RAID controller and can't use it.
Thanks in advance!

Best regards