From what I can find from public domain sources, I don't think you'll be able to make that connection. Wikimedia Commons shows this interesting picture, http://commons.wikimedia.org/wiki/Image:Rimini135.jpg, which shows the Malatesta line through the younger Sigismondo dying out. I can't make out the date on that picture though when it says it died out. Any connection to the family looks like it would come through Pandolfo I, son of the founder of the House of Malatesta.
FamilySearch.org shows lots of possible Malatesta connections. You might also try looking into a subscription to genealogy.com if you're really serious about finding a connection.
