Hi, roscoiii. Rigidly coupling refers to cones, spikes, roller bearings, bolts, whatever rigidly couples.
I suggest using spikes or cones when you want stiff lateral stability, like rack to floor and loudspeaker through carpet to a concrete foundation. With individual components on a rack, it's been my experience that isolation/decoupling is better if you're employing excellent materials for the job. In the past, cones had often worked better than other alternatives because there were virtually no excellent compliant materials for the job. That's no longer the case, though.
Audio components have unique vibrational problems. It's mostly higher-frequency micro-vibrations that you cannot feel or detect that cause most of the sonic glare, harshness and other anomalies. These energetic vibrations travel readily through hard materials and rigid interfaces.
Common and industrial off-the-shelf vibration-control products are not formulated specifically to address audio's particular needs. A rubber formulated to reduce vibrations of a workbench motor will have little affect with an audio component and is more likely to give ill affect. Likewise, materials that are good at absorbing shock in a shoe aren't necessarily going to quell the micro-vibrations that disturb a capacitor. By the same token, Herbie's materials that are formulated for audio systems probably wouldn't be great as a jogger's shoe insert.
With audio components, I believe vibration damping is the way to go regardless of the quality of the rack. Virtually every audio rack is less than ideal.
Footers between component and shelf are usually the primary isolation. I would consider interconnect dampers and Stabilizers as supplemental.
There's a thread further down called "coupling vs. isolation" that also touches on these issues that you're asking about.
Good luck with your system, and I'll hope to be hearing from you again.
SteveHerbie's Audio Lab