Heat oven to 350° (325° for dark or nonstick pans). Grease bottom and sides of rectangular pan, 13x9x2 inches, with shortening or spray with cooking spray.
Reserve 1 cup dry cake mix for filling. Beat remaining cake mix, the butter and 1 egg in large bowl with electric mixer on low speed just until dough forms. Press on bottom of pan.
Beat sugar, cream cheese and vanilla in large bowl with electric mixer on medium speed until smooth. Beat in remaining 2 eggs, the sour cream and 1/4 cup of the whipping cream on low speed until smooth; reserve 1 cup cream cheese mixture. Pour remaining cream cheese mixture over crust.
Beat reserved 1 cup cake mix, reserved 1 cup cream cheese mixture and remaining 1/2 cup whipping cream in same bowl on low speed until smooth. Drop chocolate cream cheese mixture by spoonfuls over cream cheese mixture in pan. Cut chocolate mixture through plain mixture with knife in S-shaped curves in one continuous motion. Turn pan 1/4 turn, and repeat for marbled design. Tap bottom of pan sharply on counter to level cream cheese mixtures.
Bake 32 to 40 minutes or until sharp knife inserted 1 inch from side of pan comes out clean (center will not be set). Cool 30 minutes on wire rack. Refrigerate 30 minutes. Run knife around side of pan to loosen cheesecake. Refrigerate at least 4 hours until chilled. Store covered in refrigerator.