Changing the video directory won't change the Data Path.
Open regedit.
Navigate to Squaresoft, Inc.
And Final Fantasy VII.
Check "DataDrive" is set to the CD drive you are using.
If that is right and it still doesn't work, trying making images of each of the discs with ISOBuster, downloading DAEMON Tools and mounting the image to a virtual drive, then going back and changing "DataDrive" to the virtual drive letter.