multiple drivers unnecessary for headphones
I can see the point in having a separate bass driver but here's a little insight, humans only have two ears.
The reason why two speaker DSP based surround systems for your TV aren't as good as proper multi-speaker setups is because you can't ensure that each ear hears exactly what you want. With headphones it's a given so DSP based surround should be perfect.
I also can't see that placing drivers slightly forward or backward on an earpad is going to make the listener believe they are hearing sounds from infront or behind. Therefore is these headphones are producing a surround effect, which the review says they are, they must also be using some kind of DSP processing.