In a large bowl, mix together the berries, 1/4 cup sugar, and amaretto. Set aside to macerate for 15 minutes or up to 1 hour at room temperature.
Meanwhile, make the zabaglione: Set an instant-read thermometer in a cup of hot water. In a metal bowl, with a whisk or a hand-held electric mixer, beat together the remaining 1/4 cup sugar, egg yolks, and Marsala until well combined. Set bowl over a saucepan of barely simmering water and beat mixture until tripled in volume and thermometer registers 140 degrees F, about 5 minutes. To ensure that eggs are cooked, beat mixture 3 minutes more. Set the bowl in a bowl of ice water and continue beating until chilled.
In another bowl, beat the heavy cream to stiff peaks. In 3 additions, fold the whipped cream into the zabaglione and store in the refrigerator.
When ready to serve, divide the fruit among stemmed glasses or bowls and spoon the chilled zabaglione over the top. Serve.