Like you, have been searching for a recipe for Macaroni's Tiramisu forever. Since it's been 7 months since you posted a request, I hope you see this. Maybe it will help someone else looking....

The only luck I ever had (and I've looked everywhere I could on the net) was this...a message board response ages ago by a Rudy2 at Idunno.com. The website no longer works from my server. Here is what I copied from Rudy2 (He sounded credible:

"I can only tell you the ingredients of the Tiramisu from Macaroni Grill, if you are willing to experiment with amounts. You are correct, their Tira is to die for!

Hot Expresso Coffee
Meyers Rum
Brandy
Kahlua
Ladyfinger cookies, dipped into the above mixture. A combination of Marscapone cheese (Italian Cream Cheese, which can be faked with Philly Cream Cheese and Sour Cream), and Zabayone Marsala Merinque.

Layer the cookies and cheese/meringue misture to fill your baking pan.

Don't bake, just cover with plastic and chill."

As for myself, I keep hoping someone else will compute the measurements, so I can just make it and enjoy.