i wrote this to illustrate that, even with the efficiency of the Axiom speakers, the power needs for good reproduction of (mainly) movies is higher than we often suppose. 10 Watts or 100 Watts per channel is, in most situations, simply not enough power to give a crystal clear rendition. ...
I don't have the time or energy to track down the difference between what you found and what is offered up in the standard formula for calculating power requirements.
Based on my experience to date, I'm still siding with the traditional calculator. My original receiver was rated at 90 wpc two channels driven and delivered crystal clear sound up to unreasonably loud levels (pushed it to 90db briefly one afternoon).
It can't hurt to have 300 wpc, but really, unless you have a very large space, its not needed.