xine-lib cannot handle opus audio in ogg container. It can play opus audio in mkv/mka container. The issue is confirmed by several users. There is more information in forum thread: https://forums.gentoo.org/viewtopic-t-1085726-highlight-.html
(Unfortunately I'm unable to create an account at xine bugzilla, their website seems to malfunction. So I'm reporting it here, in hope it gets attention. xine-users mailing list seems to be dead, too.)
I tried with latest xine-lib-1.2.9 from their mercurial repo, no difference, the problem is still there.
The mailing list seems to work, here is your post from 2 days ago:
(In reply to Jonas Stein from comment #2)
Yea there is my post alright. So technically the list is not dead. Without active members it isn't alive, either.
I really Like Quod Libet, but what use is a music player which cannot play half of my files?
How about adding VNC backend to the Gentoo ebuild? More choice is better, right?