I think it's a good one, but you shouldn't buy a6pro only for only the physics engine. you can also try newtongamedynamics if you don't have pro, but I don't think ngd is much better.
Thanks Roel, for what I've been able to gather from this Forum is that A6 is really a solid software. A6 and a modelling/character building program should be enough create what I've in mind.