Everyone has his own preffered flow, but one thing should be kept in mind.
Both Prefab3D and AwayBuilder are made for real time 3d and Away3D in particular. Both run using Stage3D, which give you a very clear idea on how it will run in your final project.
If your project is relatively “big”, it is almost certain, that you will have to spend extra time if you build the project entirely in max, blender, maya etc because their purpose and the way they handle the data is very different than how Away3d will handle it in the end. In fact that’s why all the engines for Stage3D such as Flare3D, Minko etc have dedicated editors.
So I would recommand focus on how to bring data to these apps instead of way around.
“there is no option for outing the 3DS file”
Awaybuilder focusses on awd and has no export feature.
Prefab has exports to AS3 for Away3D 2.0 to 4.1, obj, ac, asd, md2, awd1.0,awd2.0, ThreeJS, DXF and STL. 3DS import is supported, but there is no export to it yet.
“I export an object to “AWD” directly by 3D MAX? “
Yes there is a plugin, look on awd page, but its for 11 or 12 version of max, and export is awd 2.0. But you could export as obj of collada too…