I'm not sure about how to go about this with RAID, but you need to delete/uninstall your IDE Channel.
On a non-RAID system, one can restore UDMA usually by using the uninstall option on the Primary or Secondary IDE Channel in Device Manager. With RAID it will most likely be different, but see if there's something similar for the RAID that can be uninstalled (perhaps the controller?).
JigPu