The Symposium Osiris Stealth Ultimate high end audio rack with optional OFC (Oxygen-Free Copper) Leg System.
Symposium writes: “The leg system of an audio rack is of vital and primary importance to performance. The rack support frame affects all aspects of sonics, including bass, imaging, harmonic integrity and more, through its capacity to efficiently drain vibratory energy to ground while serving as a damping load to the shelf system. 

To that end, all of our racks have employed solid aircraft aluminum not just because of its enormous strength and rigidity, but primarily because of its high mechanical conductivity. In this critical regard, aluminum is superior to wooden legs and all hollow or chrome-plated tubing. Filling hollow legs with lead shot or sand does not improve mechanical conductivity, but is done to damp the pronounced resonances of hollow tubing, something that isn’t a concern with solid aluminum or copper legs (they are massively self-damped and acoustically “dead”). Ultimately, copper is the best support material available (the only metal in nature superior to copper in this function is silver), and of all available types, oxygen-free copper is the purest available copper. This semi-precious alloy is available for the Osiris’ Legsets, Top Caps, and Cone Foot Terminator elements, hand-polished to a lustrous finish that enhances copper’s natural beauty.

Note that all Rollerblock Modules in OFC Osiris Racks are supplied in a special edition, polished 7075 aluminum version (as shown in photo at right). 7075 aluminum is a premium grade, super-strength alloy chosen for its performance under high weight loads.
Note: Do not confuse copper plated legs with solid OFC legs! Copper plating is decorative only; solid copper is markedly superior for audio performance.”