Using Scene Assembly in Maya out of the box is very complicated. There is currently only Pipe Assembly Manager in Maya Bonus Tools to help dealing with the setup of Scene Assembly, but it's broken for OSX and Linux.
Here is my take on making Scene Assembly usable. We already used it in production several times and it has been a great helper.
Scene Assembly Manager is available for download at braverabbit.de/sceneassemblymanager/ but without any promised support.