What settings do I need to change in the BIOS?
There is only one setting that needs changing. If you were previously fiddling with other settings in the Boot tab, press F5 to load the optimized defaults. Then navigate to the Advanced tab and look under the Onboard Devices Configuration. Change the PCIEx8_4 and M.2 Configuration from Auto to M.2.
For Samsung XP941 owners, you're stucked with UEFI. Since the UEFI driver is embedded into the firmware itself, you will have no problems installing in this mode. The problem arises when you want to do a legacy installation because it requires a driver to be loaded during the installation process. With the XP941 being an OEM product, there are no drivers available to install in legacy mode.
http://rog.asus.com/forum/showthread.php?53091-Rampage-V-Extreme-M-2-Setup-And-Windows-Installation-FAQ
Und CSM darf da AFAIK im Bios nicht aktiviert sein:
http://rog.asus.com/220572013/rampage-motherboards/rampage-iv-uefi-boot-installation-guide-on-windows-7-or-8/
Und nen Treiber kannst du da definitiv knicken.