I found C19 Ultra can be modded to C19 SLi XE!And I done the test!Because I don't have the dual GPU card,so I can't do the C19 Ultra to C19 SLi XE modding,but I have done the C19 SLi XE to C19 Ultra mod!This link below is our test!
http://www.hardspell.com/hard/showcont.asp?news_id=21876&pageid=6852
http://www.hardspell.com/hard/showcont.asp?news_id=21876&pageid=6852