I just installed a Samsung 840 Pro SSD in my box, NOT as the system drive, but just as a regular HD. I have a Gigabyte board[*] with 6 SATA ports in an Intel controller and 2 additional ones in a Gygabyte controller; I plugged it into the Gigabyte controller, which was set in the BIOS to work in IDE mode, and things worked pretty well. However, Samsung Magician 4.1 warned me that the drive wasn't in AHCI mode, so I went into the BIOS and changed the Gygabyte SATA controller to work as AHCI... and now everything still works, but Samsung Magician can't detect the SSD.
The software says that "no Samsung drives were found on the system"; the funny thing is, you can select the SSD in the software's disks dropdown, but it will treat it as a regular drive, without giving any additional information nor any options. This means that I can't check the drive's health, nor upgrade its firmware.
Anyone knows what's going on? (This is all on Windows 7, BTW).
[*] A Gygabte GA-P55-USB3, to be exact.