I think you don’t need to set the cubeMap property, only the envAtlas one. But you do need to set the cubeMapProjection property in additon and provide some metrics for your scene.
Like this example does:
roomMaterial.cubeMapProjection = pc.CUBEPROJ_BOX;
roomMaterial.cubeMapProjectionBox = new pc.BoundingBox(
new pc.Vec3(0, 200, 0),
new pc.Vec3(400, 200, 400)
);