2.5mm Balanced Audio Cable For Sennheiser HD 2.20S 2.30i 2.30g HD 560S headphone | eBay
Sennheiser HD 600/650/660S Cable 6.3mm/3.5mm/balanced 4-pin - Etsy
Amazon.com: TW-TW 2.5mm Trrs Balanced Male for HD580, HD600, HD650 etc. Headphones, for AK100II, AK120II, AK240, AK380, AK320, DP-X1A, KANN etc. (1.5M(4.9FT)) : Electronics