Some AV receiver can’t use tape loop for digital input sources.
If your TV has analog audio output ( usually a 3.5mm phone jack ), connect the TV via a 3.5mm to rca cable instead of digital optical.
Maybe you can use the internal AM/FM tuner to test the Kube via Dat or Tape loop.
Maybe you can use the internal AM/FM tuner to test the Kube via Dat or Tape loop.