In same bowl, beat reserved 1 cup cake mix, reserved 1 cup cream cheese mixture and remaining 1/2 cup whipping cream 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 one-quarter turn, and repeat for marbled design. Tap bottom of pan sharply on counter to level cream cheese mixtures.