I have to say, for a price / performance deal, that zalman reserator is a recommendation I'd make to anyone for passive cooling. The only downside is if you can't do it with that tower, you need a different system. no expansion really. I mean, the system that one's on is a nice computer though. and I think they make a new reserator now, so that might be better too
Otherwise, if you look at the prices of passive cooling components available, it's really worth it to get one of those triple-120mm fan things, and run it slower for low noise.