The Stax SRD-X Pro is a driver unit designed to work with Stax electrostatic headphones, which require a dedicated power supply to function. This specific model is a step up from its predecessors, providing improved sound quality and additional features. The SRD-X Pro is equipped with a high-voltage transformer that boosts the low-level signal from standard headphone outputs to the high voltage required by electrostatic headphones. The unit has a built-in volume control for easier volume adjustments. It's designed to accept inputs from various sources, including portable music players, and is suitable for audiophiles seeking to experience the unique sound signature of Stax electrostatic headphones. The design typically includes a durable chassis with a sleek aesthetic, along with standard features like a power input and speaker output connections. The SRD-X Pro is compatible with a wide range of Stax headphones, making it a flexible addition to many audio setups.