It’s designed to work directly from a computer USB interface. I suspect it won’t be recognised by the TV box USB port hence why you have no sound. Toslink or Coax from the TV Box digital output will be needed instead.
From the manual - When connected to a computer via USB, the DAC-V1 will behave as an external sound output device and be accessible to a wide variety of audio playback applications.
I think the above will be correct regarding your TV’s USB plug not being an audio out. I use optical cable (Toslink) from TV to DAC.
You may already know the rest, but just in case… Until recently I used the DAC V1 as a pre feeding into my NAC282 and it worked well. The DAC was fed by dedicated streamer/server boxes via its USB output (i.e. you are not limited to standard PC’s). Control is easier with the volume fixed in the settings (especially if you have a Naim pre, because the remote works on both). That fixed volume is overridden as soon as you plug in headphones, then goes back to fixed when headphones unplugged.