Supported 3ds Max Materials
The 3ds Max Physical Material is supported in Arnold. It translates to the Arnold Standard Surface shader behind the scenes. However, not all of its features are fully supported, notably the "advanced" mode with a custom reflection curve.
It is effectively functionally equivalent to the Arnold Standard Surface, but using it has the benefit of being renderer agnostic, having a nicer UI, and having a good viewport representation.
A few "material management" materials such as Multi/Sub-Object, Blend and Double Sided are also supported, as well as the pass-through features of Direct X Shader, Shell Material and XRef Material
The other 3ds Max materials are not supported, and will not render with MAXtoA. You can use the Scene Converter in 3ds Max to upgrade your materials to the Physical Material.
Additional materials will likely be added in future releases.