Electrostatic tech exists in the speaker world too, and is closely related to what microphones use unlike planar magnetic and dynamic drivers. All of them will thus continue to evolve. Stax is actually one of the better headphone companies at evolving their own lineup with technology and manufacturing processes, hence the time it takes for them to release a new product (kind of like Sennheiser with the HD 800). Though the SR-009S isn't the best example of that hence the name, it's more of a retuned SR-009 as far as I can tell (like the HD 800 S). I commend HiFiMan for the evolution they showcased with the HE1000 but now I don't like what they're doing.