Make a new chor. Turn off all lights except keylight, but turn that down to about 25% intensity. Set shadows to "on" in the keylight with 100% shadow and two rays cast. Turn the ground off. In the camera properties change the standard light blue color to black. In the chor properties change the Global Ambiance type to "Global Color", this is in AM V.15. In the submenu set Ambiance Intensity to around 80% and Occlusion to 100%. With these settings you should get the same results that you see here. Remember this is done in V.15, I don't remember when AO was added to AM, but it may not be included in earlier versions. Oh, almost forgot, you need to use multi-pass rendering. Set to a minimum of 9x, that works decent.