Sound power can be converted to sound pressure as you say. I think though sound power is a convenient yet incorrect term because it is sound pressure that is directly measured and not sound power. But it's really tomatoes, tomatos, potatoes, potatos.

Axiom certainly didn't say they're ideal omni-directional radiators like a pulsing sphere. Just wait though. Ian will make them more ideal by putting drivers on the top, bottom and sides...LOL!

They're omni-directional to the extent they need to be in order to satisfy the spinorama.

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