I tried to install ESXi 5.5 on my S2600-CW2 board. The installation process breaks up on ACPI initialization and boot again.
Upgrading to the latest Firmware 01.01.0005 (from 0003) didn't solve it. There is no RAID-Controller card, only the two CPUs and one USB-Stick for installing.
For the S2600-CP2 board, there is a recent version of the BIOS that works:
Any ideas how to solve it?