How can I play AOM The Titans Cross-platform? (Pc and Mac)

A friend of mine has a MacBook and I want to include him in our lan-parties (3 other guys, so we would be 4 and epic 2v2 could break down >:D), but the pirated version is not compatible so I was wondering if there's a way to include him in the Pc-'fiestas'...I saw the game is on steam, but dunno if it supports cross-platform D:...Would not want to spend $30 each of us and realize that it doesn't work :C...

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Thanks pals ;D