I have not done Physique 57. I am currently doing a P90X2 rotation. It is nothing like P90X. It is extremely challenging from a balance standpoint, not from a heavy lifting point of view. Most of the exercises are done using a stability ball or medicine ball for balance work while you use body weight or light dumbbells. Since I'm only in the first month of the rotation, I can't really comment on the entire program. I've heard that many people were dissapointed in it because they thought it would be a harder version of P90X. If that is what you expect, you'll be disappointed. I'm enjoying it because I like Tony Horton. I'm enjoying it because it's different from any other routines I have. I'm enjoying it because I'm seeing improvement in my balance (some of the exercises are frustratingly hard just because you can't manage the balance aspect).
Before you purchase it I would check out the clips so you can get a good sense of the exercises. Since you already have P90X, you know Tony and his style. He's the same in this set.
Good luck with your decision.
Kim