Make sure you remove all other lights in your scene. If you’re not using modtool versions of Softimage you should have full range of abilities in lighting. As long as you position your camera in the right spot and have your lighting properties set accordingly it should help reduce the dullness you’re wanting to avoid.

^ Something kinda like this might help give the visuals you want ^
Both your texture and mesh will also have things to play with this too. If you have a smooth high poly mesh, with less shading issues, that will boost your visuals tremendously. I’d recommend looking up some video lessons on different modeling techniques in XSI. I know it helped me a ton when I took time to figure out some different methods.
In the end, knowing more about increasing mesh, lighting, and texture quality will help you overcome this.