I'm not familiar with this, so please check the photos. It's probably the following product. Please purchase if you know about it. "HA-2" and a conversion cable that allows you to connect 2.5mm 4-pole products for AK with ground separation. As an optional cable for the DAC-integrated portable headphone amplifier "HA-2", the "2.5mm to 3.5mm 6N-OFC Balanced Headphone Converter Cable" (OPP-CC-2535BI) is used to connect earphones and headphones with 2.5mm 4-pole terminals to the ground.