Looks like there's a new bios avalible - 1101.
P5K Premium/WiFi-AP BIOS 1101
1. Support new CPUs. Please refer to our website at: http://support.asus.com/cpusupport/cpusupport.aspx
2. Fix the display priority may be incorrect when plugging two PCIE VGA cards.
Support added for:
Q8200S rev. R0
Q9400S rev. R0
Q9550S rev E0. (Bold by me)

What does 'S' means??