How do you get Beryllium to be flexible enough to use in a planar speaker? It's my understanding that Beryllium is very rigid. That's why it's used for tweeters. AFAIK Beryllium is not used in with planar speakers. FWIW: I have M-560's and M-300's. I also have planars (Magnepan 1.7) for my main speakers.
These are quite impressive headphones but suffer from a few flaws. The headband is way too large making them suitable only for those with big heads. The mid-bass is overemphasized to the point of distraction with the stock pleather pads. The cloth pads are itchy and of poor quality.
With the negatives out of the way, these are amazing headphones otherwise. These have the most detailed midrange I've heard among my collection. They are better than the M1060, M560, DT880, and HD-6XX. Treble is slightly recessed but extremely smooth. There is sub-bass but it's drowned out by the mid-bass. You can solve the issue with buying aftermarket pads but they should have come with a single good pair of pads to start with.
In short, change the pads and these are the best headphones you can buy for the money as long as you have a big head.