Griff,
You have two options.
Option 1
You can switch to a an isometric view in your ABS drawing and do an Export to AutoCAD command. This will convert your AEC objects (ducts, pipes, etc) into AutoCAD 3D Faces. You can then link in the exported file into your Revit Model.
Option 2
Do a search in your Content Browser for a "Convert to Solid" tool that converts AEC Objects into Solids. You then convert your Duct System to 3D Solids. You take those 3D Solids and export them to an ACIS file (*.sat). You can take the ACIS file and link it into your Revit Model as well.
There's no one-to-one interoperability for objects between the products, so these are your best options.
Cheers,
Kyle B
RSY Product Support
Kyle Bernhardt
Director
Building Design Strategy
Autodesk, Inc.