Well depending on what you want to spend I can see a few options.
1) As for the pump, sell the K Nano and get a Vortech MP10. No need to touch the return pump.
2) Go with a Metal Halide setup over the tank with a good bulb like the Phoenix 14K.
I currently have a Hamilton Tech MH fixture over my Nano Cube. It is the 150W version and I have upgraded to the Phoenix bulb. I also built a screen that goes over my tank so fish can't jump.
Here is a picture:
I will be selling my setup here in the next couple weeks if you are interested in the light. Right now I am in talks with someone about the light. If they back out I can let you know.