This USB connection on the rear of the AXA35 is designed for charging or maintaining power to a gadget such as a Streaming device or Bluetooth adaptor.
However, please be aware that we do not advise that you use this port for charging a device and using it as a source at the same time, as this will create a ground loop that will cause interference during playback. This is due to the nature of the circuit ad components used in the AXA35.
Please note, this port is not an input so will not allow you to play audio directly to the unit.