Ben, welcome. In my view the perfect Axiom speaker already exists, and that's the M22 sound that I've enjoyed for over 6 years now with lowest bass being reinforced by a sub on some material. The M22s, even without the sub operating, have good bass down to about 50Hz with room reinforcement, which is adequate for most music. With a good sub such as the EP500 the lowest octave is covered well for pipe organ and some movie LFE. Adding a 6 1/2" driver instead of the second 5 1/4" wouldn't necessarily make a significant difference; many factors besides simply the size of the driver are involved.
