PCM optical output

Is there a way to select PCM optical audio output from the set-top box?  There is an optical port, but I believe it is not delivering PCM audio throught the fiber.   I can't find a way to select this output format, but I have a Vizzio Audio Bar and it requires PCM audio.  Analog audio with conventional analog output signals are decent, but not anywhere near what optical PCM could deliver. This could be configured through a software update since the hardware and diode are working fine.