To connect a subwoofer to the ADAM D3V, an external audio interface is required. The D3V's USB-C input is a digital connection designed solely for direct communication with a computer; it cannot be used to integrate a subwoofer into the signal chain. Therefore, you must use the D3V's analog TRS inputs.
Setup Steps:
Connect the outputs of your audio interface to the inputs of the subwoofer.
Connect the outputs of the subwoofer to the analog TRS inputs of the ADAM D3V.
Note: For further details, please refer to pages 8–9 of the user manual.