Materials matter, but are meaningless if improperly implemented. The hugely popular B&W Kevlar mid-range looks fancy and because of their marketing they have sold many of them, however these drivers are far from pistonic in operation. Kevlar alone is ironically one of the worst materials to make a midrange driver out of, as it has a significantly lower modulus of elasticity (in single digit GPa depending on the composite layout) than aluminum (about 70GPa). Kevlar is also pretty heavy in comparison to paper, much less aluminum and PP, and therefore puts a lot of extra force on itself when moving at the incredibly high acceleration a midrage driver undergoes.
So in fact, the "last century" material of paper outdoes the "high tech" Kevlar in both stiffness and lightness. So why does B&W use it? If I had to guess, it's because Kevlar is very strong. I have seen Klippel scans of B&W's Kevlar driver, and they clearly operate almost entirely in breakup (aka non-pistonic). However the high strength of Kevlar keeps the cone together and allows it to take more of a beating (more force, more wattage). Unfortunately, operating in breakup introduces a lot of distortion.
Magico's drivers on the other hand are actually well designed with fancy materials, but they have had to put a lot of effort into developing these designs. The real reason why you don't see more "fancy materials" in these high end speakers is because it's incredibly hard to simulate anisotripic material behavior. So either you spend millions on empirical testing (arbitrarily designing a driver, measuring it, then making a slightly different driver and testing it then comparing the difference), or you find someone who has developed software or has experience in the behavior of anisotropic materials. And even with all that, Wilson and Vandersteen speakers are still competing in the same realm as Magico. So is all that R&D worth it?
Also @johnk , carbon nanotubes are only dangerous if inhaled, they are inert in Magico's application. The same danger is present in Beryllium, as is toxic when inhaled in powdered form but inert when in a solid dome. Additionally, plywood actually is superior to MDF when implemented correctly, as it is stronger and stiffer. However, it is anisotropic, so it is tougher to design with and requires more expensive manufacturing techniques. As you can see there is a common theme here. The reason why so many manufactures use these "old" materials is because they are generally isotropic, and therefore are significantly easier to design with. When your material has relatively constant properties in all directions, your only variable is geometry.
Also die casting refers to the use of a permanent mold, not to the quality of product being produced. Die casts are used as opposed to green sand or investment ceramic molds because they are reusable and highly repeatable. That's why both speaker designers and Hot Wheels would use this method to produce metal parts.
There is also the whole thing of defining "good sound" and whether or not certain materials actually produce "good sound" or whether we perceive them to sound pleasurable. But that is an endless can of worms that we should save for another discussion.
