We agreed to play Heroes of Might and Magic III online! (July 2010 - December 2013)

I want to play, but there's a problem... I have the "Platinum" version of Heroes (without Chronicles or In the Wake of Gods)... and it seems like everyone else has SoD...

The "Platinum" version is perfectly compatible with SoD. In fact, many people have the Platinum version, as far as I know.
P.S. I can play in War of the Titans, even without experience, or SoD with an experienced opponent. 442018688.