Hmm. I narrowed down the problem and found a workaround.
I had this exact same symptom after a previous iTunes/QTime install and part of the debug suggestions that time was to verify the content played back in QTime player. That time it did.
However, when I tried it in QT player this time, to my surprise, no sound, just like in MC.
Searching the net to try to get QT player to work, I found others with the same problem, but no luck. But some were suggesting to run in compatibility mode (which does NOT work), and this led me to think about their ongoing battle to protect the DRM content and it occurred to me that maybe they set it up so that the application needed special access...
So I ran QT player as administrator and... sound!
I leave QT player running and launch MC and try... no sound.
So I try launching MC as administrator... SOUND!
Geez.
In my particular case, this meant browsing to:
C:\Program Files (x86)\J River\Media Center 12
Right clicking on Media Center 12.exe and select "Properties". Click on the "Compatibility" tab, then select the "Run this program as an administrator" checkbox. Click "OK".
Now my iTunes DRM content works under MC again.
sigh
-john