Talk to your dermatologist
Differin is for acne. Pro X is a pretty heavy line for aging skin. Odds are if you use the Pro X and have acne, the acne will worsen. There are other, better combinations for aging skin that has acne (Retin A and Tazorac, for example). That said, talk to the dermatologist who prescibed the Differin because you might have a unique situation.