If you only upgrade one component in HT what is it

Pre Amp, Amp , DVD player?

I am looking to upgrade one component in my home theater. Where will I see the biggest bang for my buck. I have the Mitsubishi 57" Diamond DLP using wire world Silver squared flat HDMI, or Purist Audio Design Component with Ferox as interconnect. I have Sunfire TG II and Cinema Grand, Sony s9000DVP as DVD/CD/SACD, I also picked up a Denon 357 to try 1080p upscaling.

Any thoughts on what will make the best mose noticable Audio/Video change. My system is both my HT and 2 Channel. B&W 804s, HTM3S center each with Synergistic Spec 7. Sunfire sig sub and VR-1 von s rear. All interconnects and cables are maxed for my budget (all Synergistic and Purist Audio)

Thanks