One big difference is the addition of a new four-model structure with Tour (T) Players (P) Extreme Forgiveness (XF) and Super Game Improvement (SGI) now offered. But the real design difference has to do with the a new material used in the clubs that produces more speed and distance among other things.
Thomas has long used Titleist equipment but he has made some changes since his last PGA Tour win. At the Honda Classic in February he used a Titleist 917 D2 driver and a Titleist 917 F2 fairway wood.
The big differences between the AVX and the Pro V1 and Pro V1x is the spin rate trajectory and feel it provides. The AVX is the lowest-spinning and lowest-flying of the three models and it also offers the softest compression.