Power = Current * Impedance², too. I don't see how that's relevant to the subject here.
Without any knowledge on the gain, you won't go too far with the maths.
Also, power is not the real player here. Current delivery is. Unless you listen at crazy loud volume, you'll never go anywhere close to 1W in power need.
The thing is: powerful amps usually have the current capacity that goes with it (obviously, otherwise distortions would be very high), that's the reason why high power amplifier are always recommended. But having a high power output is not a must to get the surge current capacity the headphone needs. Look at the typical Brit amplifiers: there not that powerful in term of pure wattage (advertised); but man do they deliver in terms of current (which makes their very good PRaT performance)!
Power dissipation might be a reason why the Bakoon can only deliver 1W continuously. Anyway, there's really no reason for an amp to provide 1W of continuous power into a headphone (unless you want to use it as desktop speakers...).
An amp can well be designed with a 250mW maximum output but with a very beefy power supply that can provide lots of current and won't weaken during surge current. A amp can also be designed to provide 6W of continuous power but with a lesser ability to sustain during current surge (which results in high distortion level).
I've found underpowered amps really don't work well with the LCD-3s....and the LCD-X's aren't as particular. Simply delivering current without the ability to swing voltage for complex music can really not help the drivers and the LCD-3s can come off as too laid back. Again, this is based on my first hand experiences and I was mentioning that I wasn't surprised that the more efficient LCD-X worked better with the Bakoon thank the LCD-3s.