Which One Do I Have To Have?

If I understand you correctly, you are contemplating between a power conditioner and a system cabinet. Before I got my Monster Powerbar 2100, I was using well insulated cables for my analog signal from my cable company. There was some snow effect. When I received my power conditioner, it seems that the AC noise gotten filtered, thus, no more snow effect. Similar to your case, I don't have enough shelf on my audio rack. Hence, I hang the Powerbar on the wall next to the rack. You can always use something better than the Powerbar for your audio gears. In my case, picture quality was the top priority since so much money was spent on the plasma.

I'd think about running a dedicated circuit for the Marantz piece :^)

I've got the Monster 5100 power center in my HT. All I can tell you is that, for me, it improved picture quality tremendously. I was quite surprised at the improvement. I expected some, but nowhere near as much as I got. It didn't seem to help the sound as much, though. Just don't even think about plugging an amp into it. That WILL affect the sound, and it won't be good.