I've never seen this before. The BIOS reads SATA as ACHI. I cannont swith to IDE unless I re-install the OS. So Is this Windows (WIN 7 PRO x64 installed), or Is this an Intel Issue.
For converting ACHI to IDE without reinstalling the OS you might want to take a look at this link: http://www.vistax64.com/general-discussion/271218-switch-ahci-ide-tutorial-howto.html.