ok so sounds like you have the active midplane that supports both SATA/SAS. this midplane is its own 8 port sata/sas controller and offers no jbod mode to release single drives to BIOS. try configuring a single drive as its own raid 0 to release to the BIOS (F2) and OS level.
see page 13 of pdf
http://download.intel.com/support/motherboards/server/sb/d31972002_sr1550_user_guide_092506.pdf
