In a small heavy saucepan, combine 4 ounces semisweet chocolate, the dark chocolate, cream and cheese. Cook and stir over low heat until smooth. Transfer to a small bowl; cover and refrigerate for 3 hours or until firm enough to shape. Shape into 1-in. balls and place on waxed paper-lined baking sheets. Chill for 1-2 hours or until firm.
In a microwave, melt remaining semisweet chocolate; stir until smooth. Dip balls in chocolate; allow excess to drip off. Roll in pistachios. Place on waxed paper; let stand until set. Store in the refrigerator.
Tropical Truffles: Stir 1/2 cup chopped dried bananas, 3 tablespoons dark rum and 1/4 teaspoon ground ginger into melted chocolate mixture. Chill and shape as directed; roll truffles in chopped toasted coconut. Cherry Truffles: Place 3/4 cup chopped dried tart cherries in a small bowl. Cover with 3 tablespoons cherry brandy; let stand for 30 minutes. Drain cherries, reserving 1 tablespoon brandy; stir cherries and reserved brandy into melted chocolate mixture. Chill and shape as directed; roll truffles in chopped sliced toasted almonds. Hazelnut Truffles: Stir 3 tablespoons hazelnut liqueur into melted chocolate mixture. Chill and shape as directed; roll truffles in chopped toasted hazelnuts.