Converting passthru xmldoc msg to type

I am trying to clean up how I handle a mix of defined and unknown msgs.  Right now I use the pass-thru pipeline to a XmlDoc message.  The MessageType property allows me to route unknown messages to an error handling orchestration.  I would like to process the known messages more automatically but cannot get the messagebox to resolve messagetype for XmlDoc.

Now I am switching on each known messagetype, creating a message of that type from the generic input XmlDoc and sending that to the MessageBox.  I would think I could call the XMLReceive pipeline to create/validate a message, but cannot figure out how to get a typed message out.  GetCurrent(…) retrieves the output, presumably with proper promotions, but how do I send it directly to the MB.  Retrieving it as an XmlDoc and sending that to the MB does not seem to be me anywhere.

Any help or direction?

Doug