Burning in?
I don't know what it is, but it realy sounds like not-a-good-idea. What is it? Like overdriving them to loosen them up or something?
I'd probably follow the manufacturer's recommendations for the use of the headphone.
Now I know this may not be hot for regular headphones (or any normal consumer joe-sixpack audio stuff) you'd get from any store, but if they are high(er)-end devices then the manufacture generally REALY REALY knows their stuff and it's best to follow their advice.
But then again, I don't know what burning in headphones mean anyways.