I'm sorry but I don't understand what AltDiffuse node is. I just jumped from P4 to P6 and I am so lost! So I wanted to try it right away without reading the whole damn manual first. ;-) I bought a P5 only set, DesignerLivingRoom, from Ratracer at RMP so I could just install and render - at least that's what I thought. The light set and cameras came with the product so it should work shouldn't it?

It does render lighter as in the area render above. It's just that it's too dark to see in the preview. I'll try some other lights as you suggested also.