I'm looking over that and I want to take another look in a while to be sure that I'm seeing what I think I'm seeing. Right now, though, what I think I'm seeing is small noise level changes that are 60-75 dB below the signal. Noise 60 dB below the music is usually inaudible unless you're listening for that noise and you know what to listen for. Most humans wouldn't notice a 1.5 dB change outside of an A/B test. And as Tyll points out on the next page:
My hiking boots break-in; my sneakers break-in, too. But my hiking boots aren't going to turn into sneakers over time. This idea that you simply must let headphones break-in before you know what they are going to sound like is a myth. And this data busts it.
So... do you need to break in your M-100? No, you don't. Put them on and enjoy them out of the box. And if you don't like them then turn the volume down a bit and give them a week or two to grow on you. And if you still don't like them then maybe they're not the cans for you.