For YafRray must use the free Blender or Wings3D for use it :)

And yes you must export as OBJ file for Kerkythea (seems this last has the "free" more easy interface )
Remember have some problem to load the OBJ files in Kerkytthea so
You must put your obj File in the folder "Models" inside Kekythea else nothing works :) Default of Kerkythea : some slowly for a rendering :)

You can also use the internal Renderer of Blender !
Maybe the more speedy (nothing to install) but maybe not the more easy (interface must be learning :)
Bon courage :)