To insert a family instance in a point in space the following Revit API method can be used:
NewFamilyInstance(XYZ, FamilySymbol, StructuralType)
Other overloads are documented here: http://www.revitapidocs.com/2016/451ee414-cea0-e9bd-227b-c73bc93507dd.htm
However, if I want to insert a duct accessory such as a damper using this method it does not attach the accessory to the duct. Even when giving the method the duct as the host element it does not become part of the duct system.
Is there a separate method for inserting duct accessories?