IXNAY ON THE RENDER PASS OCCLUSION RAY
Alright, the problem with maya's built in ambient occlusion render pass is that it offers no control over it! It's just a blanket setting that eats up render time like mad. It's about 5 times slower than setting up the mib_amb_occlusion node to a surface shader. Lame I say!
So keep with the method of setting up a render layer, piping the outValue of the occlusion node to the outColor of a surface shader. Assign it to all that needs occlusion in that render layer (play with samples value until you get a nice result) and render. Way faster.