Where can I start to improve my sound the most 2ch

I currently have an Arcam AVR300, Cambridge Audio 640C with MIT AVT3 cables going to a pair of Dynaudio 1.3SE's. I also bought a ZU power cable for my Arcam. What should I look to do next to improve my 2 channel audio?

Cables?
Seperate Amp?
New CD Player?

What will make the largest difference?

Thanks!