The Fosi Audio Box X4 combines dedicated phono preamplification with integrated headphone amplification in a single compact unit. Purpose-built MM cartridge input with low-noise signal conversion and grounding protection ensures pristine vinyl playback, while auxiliary inputs accommodate digital sources. Tube-based architecture supports multiple vacuum tube variants—5654W, 6K4, 6J1, 6J4, GE5654, 6AK5, and others—allowing personalized sonic tuning through component swapping. Dual output configuration enables simultaneous line-level and headphone monitoring. Package includes 12V power supply, documentation, and 18-month warranty with dedicated customer support.