Let me try to clarify a few things ...
..about curved objects:
When exporting Revit to DWG, tesselation is made by revit unless you export to solids. In that case, when importing the dwg in max, those solids objects are tesselated by the Max dwg import.
When exporting to FBX from Revit, curved objects are tesselated to meshes by Revit. In fact, a FBX export in Revit is goind through the same code path (or almost) as a Render in revit.
In an ideal world, Max would retain solid entities and manage the tesselation to meshes on its end, but it is currently not something possible with the existing toolsets - but we are aware of the problem.
To work around it, there might be a few strategies you could adopt. For example, you could set up a revit view where only walls and other flat elements are visible, and link that one via fbx. For smaller elements such as pipes, you could setup another revit view where only those are visible and link that one via DWG (assuming that you export them as solids). This way you would retain separate control over the tesselation of large and small objects.
...about units
Revit units are stored internally as feets. Changing max's system units as feet will get rid of the issue and improve the file link performance as no mesh rescaling has to be performed. I am not saying it is the ideal solution but that might be acceptable workarounds for you.
