Start at the beginning and be slow and methodical.
Do the audio files play in say windows media player to the Yamaha?
If they do that bit's ok and you should start an look at Tools | Options | Audio | Audio device in MC.
Make sure you've the correct output device selected and set the sample rate to 44.1 kHz for everything to start with.
Oh, and check your volume level
If they don't then look at the windows side of things with Sound | Playback and get that working first.
It's not clear what you've done or where you are from your posting.
Things that could be an issue:
You're sending unsupported file formats to the Yam.
You're sending unsupported file bitrates/channels via the optical link. (it only supports 2 channels and a limited bitrate
https://en.wikipedia.org/wiki/TOSLINK)
Some videos in my footer.
Spike