I don't have your device, so can't quite provide exact instructions. There are other Oppo owners here that might be able to help, and there are several Oppo conversations in the Media Network forum. It would be worth looking there.
First, you're going to need to enable Media Network:
http://wiki.jriver.com/index.php/Media_NetworkThis enables the DLNA server and clients, of which your Oppo is a DLNA renderer. Once Media Network is enabled (and if its enabled on your Oppo), you should see the device under MC's Playing Now. And once it is there, you either select it as a playback Zone in MC, or you can select tracks and use Sent To > <oppo name> to push music to the Oppo.
And if the Oppo can browse your MC music, MC should just appear in the Oppo after Media Network is enabled, provided no firewall issues get in the way.
See if this helps get you moving forward.