Sonosax’s official SX-R4 Plus documentation lists firmware version 4.1, dated December 2025, with support for the optional Dante board and SX-RX8+ functionality. The firmware also adds an IP address in the recorder’s web application for joining an existing network. For production sound teams, the more consequential detail is the migration requirement: moving between firmware releases in the 3.x and 4.x branches requires a factory reset, affecting recorder and user settings, along with formatting all SD cards.

The update instructions direct users to back up files and format every SD card before applying the update. That makes firmware-branch changes a data-management task rather than a routine field update, particularly for crews using the SX-R4 Plus across established recorder setups.

The SX-R4 Plus is documented as a 16-track recorder using two SD cards, with simultaneous Mirroring-mode recording for redundancy. It records uncompressed BWF files with iXML metadata at rates from 44.1 through 192 kHz, in 24-bit or 32-bit resolution, and supports 0.1% pull-up or pull-down for NTSC workflows. Four XLR-3F inputs can be configured for analog mic/line or AES3/AES42 digital input, while four additional AES3 inputs are available through a 3M MDR 26-pin connector.

The documented configuration options include a four-channel XLR-5M output card, Dante, and a Sennheiser AMBEO VR microphone connector. The optional Dante I/O uses RJ45 and is described as PoE-capable; it supports up to 16 channels through 96 kHz, falling to eight channels at 192 kHz. The recorder also supports expansion through the SX-AD8+, which can raise the system’s input capability to 12 microphone inputs, and includes independent Lemo timecode input and output with listed accuracy of 0.5 ppm.

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