The first thing you should do is set the height of your added lights to 60 inches +-, that should get rid of the pronounced light wash on the ceiling. To make the scene brighter, try switching on Photon Mapping (in the Advanced tab). If you go this route, be sure that you have a roof over the room you are rendering to avoid light leakage where the walls meet the ceiling. Another important factor is learning the functions of the Ambient Light settings (Lighting tab), I like to use Ambient Occlusion settings of .5 - 3.5 as a starting point. The rest is just experimenting to learn the functions of the settings. There are several excellent videos on the Chief website which you should watch https://www.chiefarchitect.com/search/?default_tab=video&q=ray+tracing.
Once you start to understand the many settings in the Ray Trace DBX, you'll be able to create great looking renderings.