The HiFiMan EF400 is compatible with a wide range of headphones, including both high-sensitivity in-ear monitors (IEMs) and power-demanding over-ear headphones. It offers multiple output options—3.5mm single-ended, 4.4mm balanced, 6.35mm single-ended, and 4-pin XLR balanced—to accommodate various headphone connections. For high-sensitivity IEMs, it's recommended to use the low-gain mode to prevent excessive power output.
