Dual Senn. 2-pin headphone cable for HD Series (600, 6XX, 58x & more) – Hart Audio Cables
Amazon.com: Audio Cable Replacement with in-Line Mic and Remote Volume Control - Compatible with Sennheiser HD525 HD545 HD565 HD580 HD600 HD650 Headphone and iPhone iPod ipad Apple Devices : Electronics
WyWires Red HD600: well-built, tangle free cable with a deep black background and big soundstage – Audio Primate