Round trip Rhino to Alias: recommended file format & settings

What is the recommended file format to export curves and surfaces from Rhino, into Alias and back to Rhino while retaining the layer structure?

I expected to be able to do this in DWG, however, the Rhino docs show that this format apparently doesn’t support NURBS (even though Autocad does)…

When I export .step files, the objects created in the default layer are nested in new default layers per object.

Also, how do I match these import settings? The “User Defined” settings are saved by Rhino.

Have you tried IGES? Any joining info will be lost, but maybe that is not all that important. You can look at IGES export settings, there are a lot of stock ‘flavors’ (including one for Alias) and you can customize them.