Has your MyCloud recently done an automatic firmware upgrade? If so, it’s likely to have trashed your twonky setup.
I assume your Sony TV and Bose system are accessing via DLNA (Twonky), and you have checked the directory content with File Explorer.
This might help:
http://community.wd.com/t5/WD-My-Cloud/FAQ-Twonky-DLNA-Media-Server-Setup-amp-Use/td-p/858810