Check the audio cable connections to your speakers and ensure your speakers are set up correctly.
Adjust the volume on both your computer's system audio and the Monitor knob on your audio interface.
Check the settings within the TOPPING Pro Control Center. This includes your output settings, mute status, and the hardware monitoring mix ratio if MON Hardware Monitoring is enabled.
Try connecting the audio interface directly to your computer's USB port, bypassing any USB hubs.
Disconnect any idle USB devices from your computer.
Close all applications that are not currently in use.