I am sure that I am missing some basic concept that makes establishing a layer map for export a piece of cake, so I am finally jumping in to join the forum world in the hope that someone can flip the switch for me and the lightbulb will come on

I understand how to go thru the process of exporting and I have begun to edit the layers to match the items that I can to our office AutoCAD layer standards. Where I get stuck is in the duct and piping systems categories. How do I map the Revit systems we have for pipe and duct to our mechanical layers in AutoCAD? Each has a different linetype and color, but everything is being converted based solely on the 11 OOTB Systems rather than the 18 or so we actively use.

I have looked high and low and read all of the articles/tutorials/wikifiles I can find and its truly just clear as mud to me. Please let this be just me missing the Big Picture