I downloaded an Opus test file and played it successfully, and I'm relatively sure I am NOT using Direct Show filters, because I did this on the Mac version of MC.
I was able to change it's Title and Artist within MC, but I decided to check the file itself... the tags were not written. Further, the original tags that are in the Opus file, were NOT read by MC. So the tagging support for Opus seems to be not working for reading or writing. I'm not concerned about this in the slightest. Just reporting my findings in case it helps.
Brian.