Sli is supported , but you have to instal the support code yourself and for those running Sli there is a benefit.
I have a thread in the technical area with instructions on how to instal the code supplied by Luthier (it looks like official support will never come as development was shut down before any link with Nvidia was established). Crossfire has never as far as I know been supported.
http://forum.1cpublishing.eu/showthread.php?t=37316