Winged Sonobe octahedron assembly
Image is mine. I took it for this answer.
As you have stated you can make a cube expect you can get to the point with the three pieces together. 
Which for me shows where to put the next 6. Is the adding the last 3 units the point where you get stuck?
If so i find assembling the last three pieces together and then putting them in easier.

I don't know the terminology I do know how to make a octahedron. 

Make sure all your sonobe's are the same. It doesn't matter if they all 'lean' left or right but you need 12 the same.