The chipset datasheet doesn't show eSATA support, but I don't know where else to look
Doing a Google search mostly shows eSATA on the desktop boards or the X58 workstation chipse
I might be wrong but I don't think S5500HCV has eSATA support.
Did you change the SATA controller to AHCI mode after OS installation? If so you may get error because AHCI mode needs a different driver. Did you try to install OS after configuring AHCI mode?
From my reading I quess that the board does not support eSATA. I have not tried installing in AHCI mode. I will try that when I upgrade to RHEL 5.x in May. Thanks you fory help.