I think that what you mention in terms of volume control levels could be explained with the difference of the speakers. You do not mention what the older speakers were, but suffice to say that the Axiom's seem to require more power to satisfy you. This could be explained by technical differences, and as well as pyshco-acoustical principles as well.
By what you said about needing to turn the amp louder, the Axioms seem less efficient than what you had been using. As Axiom's are quite effecient, and not knowing what you had, I am more inclined to say that the pyshco acoustical (you want to listen to them louder, as they sound better) is what you may be experiencing. The change you notice on the volume control may have been masked by the quality of your old speakers, and is a point where the amp simply produces more power in a non linear fashion.
