The Sonifex CM-HPX1 passive headphone volume control allows you to connect a stereo balanced line input via 2 female XLRs using the StudioHub+ pinout to create a headphone output with level control for any headphone over 150 ohms impedance. Transformer balanced at a ratio of 2:1 your ensured that any headphone load the unit is presented with is reflected to the input at a 1:4 ratio, suitably loaded for a good quality line output stages.