This issue occurs because the optical output signal is not PCM. (Libratone speakers only accept PCM)
The signal could be raw DTS or Dolby Digital.
Typically the optical sound signal is send to a TV box with a decoder that converts the digital TV signal to PCM. In this case the raw TV signal is sent directly to the speaker which is not able to decode the signal.
Solution: In TV settings please change digital output signal to PCM.