Sennheiser RS120 Wireless RF Headphones with FiiO D03K (D3) Optical Audio Connection Kit Three selectable RF channels in choice of 2 separate UHF groups with over 300' transmission range, reception through walls and ceilings Lightweight, supra-aural open back headphones with padded earcushions and headband, extended LF reproduction Transmitter with metal cradle for storing and recharging the headphones, easy-access controls for simplified, intuitive operation Rechargeable NiMH battery operation for headphones with 20 - 25 hr. battery life FiiO D03K Digital to Analog Converter Kit with Gold Plated Optical Cable allow easy connection to optical audio.