AHCI can be enabled. As the 840 Pro is a latest series SSD I'd recommend flashing the latest bios because 18.1 is 2nd release bios and current is 18.8:
http://www.msi.com/service/download/bios-19054.html
[URL=http://forum-en.msi.com/index.php?topic=108...
http://www.msi.com/service/download/bios-19054.html
[URL=http://forum-en.msi.com/index.php?topic=108...