I haven't worked with the P5B, so I'm just guessing here, but I suspect that two of the four plugs in the group are wired straight to the motherboard's chipset, and the other two get routed through a helper chip called a "PHY." Can you try the DVD drive on the two vacant SATA plugs that are in the group of four, and see if one of them results in it not hassling you with that message? 🙂