What is the coaxial jack for? Is it for coax SPDIF?

The coaxial fiber is for input (IN) only, used in transmit mode, primarily for TVs. It is used for playback via optical fiber when paired with Bluetooth TX and switched to COA coaxial mode.

Questions & Answers: IHDAPP Bluetooth 5.3 Transmitter Receiver, 2-in-1 Bluetooth Adapter HiFi Audio Bluetooth Receiver, DAC Converter with LED Display RGB Light and NFC 3.5mm AUX RCA Optical Coaxial USB for PC/TV/Car

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IHDAPP Bluetooth 5.3 Transmitter Receiver, 2-in-1 Bluetooth Adapter HiFi Audio Bluetooth Receiver, DAC Converter with LED Display RGB Light and NFC 3.5mm AUX RCA Optical Coaxial USB for PC/TV/Car

Bluetooth 5.3: Experience superior audio with our bluetooth transmitter receiver, featuring the Bluetooth 5.3 chip for double the transmission speed, enhanced compatibility, and stability.Long-distance transmission of 20 meters, full coverage.
Dual Functionality: 2-in-1 design works as a Bluetooth transmitter and receiver. Enjoy receiving mode that allows connection to 2 smartphones simultaneously. Supports USB disk Playback and transmission, supports up to 64G.
LED Display: Equipped with a crystal-clear LED display, provides full-screen visibility of the working status and Bluetooth modes.
Multi-Interface Support and High-Definition Microphone: With an integrated digital-to-analog chip, supports a variety of interfaces including digital optical, coaxial, 3.5mm AUX, and RCA.
Long-Lasting Battery and NFC Upgrade: The built-in 1000mAh rechargeable lithium battery offers up to 12 hours of continuous music play with a quick 1.5-hour charge. Enhanced with wireless NFC touch pairing.

$28^.99 –