Hey!
Robin/satfrat your rack is full of heavy stuffs there. The photo perspective angle make it looks like it is almost up to the ceiling! 
Take care,
Buddy 
That picture was taken last summer when the HTPC was bare. I now have a Hammond choke in the back, a Channel Island VDC-SB power supply sits up front on top of a Sony burner and a Trends UD 10.1 USB Transport sitting up front on top of a 750G exterior hard drive and in the middle of all this is a stack of marble & maple that raises a KingRex power supply/Shakti Stone/Acoustic Revive RR-77,,,,, all stacked to a height of 6.6'. The damn thing's highter than me. hehehe

When you have a component rack in close to your loudspeakers like I do, you need shelves that will not only isolate the component from the rack itself but shelves that will drain what energy they're obsorbing. Sanus uses a duel compound in drilled holes on each corner of the shelf that sits on spikes attached to the steel rack. It's said that these 2 compounds both isolate the shelves from the steel rack but will also burn off energy that the shelf itself is obsorbing from soundwave vibrations.
I think the worse thing you can do to components is place them in an unvented cabinet. Components need to breathe & vent,,,,,, just like me.

See ya soon Buddy.

Cheers,
Robin