Axiom sort of has an M66. It's the M50. I really like it. I am not sure if acoustically, there is anything to be gained from turning it into an M66 which I understand to be the same driver complement but a hexagonal cabinet similar to the Brystons and stand-mounted instead of a floor-stander.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated