Ryan,
You asked, "What are the differences between coupling the pre as Matt does, and isolating with isofeet or something similar?"
There are 3 sources of vibration: physical contact with the rack/floor from speakers, footfalls, etc.; through the air from the sound generated by the speakers; and self noise.
And there are three ways to try to address these vibrations: isolation, damping, and draining. If you think about it, all electrical components are cantilevered from the circuit board or mounting plate. This is the worst possible structure for controlling vibration (like the springiness of a diving board). And the elements inside tubes are cantilevers within a cantilever. Exposing them looks cool, but can lead to even more vibration related issues. Hanging cabling is another example of poor vibration control.
Isolation is probably the most effective method for reducing physical contact and airborne vibrations, but can’t be applied to self-noise. It’s primarily how vibrations are controlled coming and going from studios and listening rooms. Self-noise is a huge problem in speaker design as some estimate that over half of the sound emanating from a poorly braced speaker comes from the cabinet itself. Using an enclosed rack should reduce vibrations transmitted via the air, but moving equipment out of the room would be better.
Dampening involves conversion of the mechanical energy into heat and often additional mass. Coupling mass normally results in lowering the resonant frequency and increasing the amount of input energy needed to begin a resonance. A sand bag on top of your CDP or use of tube dampers are classic damping solutions.
Anything with a spike represents the draining approach. Spikes increase the bearing stress and therefore improve energy transfer. If you're on a concrete slab and using a solid/spiked rack, draining is the way to go, otherwise it’s a crap shoot depending on the construction of the floor. BTW the earth itself vibrates at 1 – 2 Hz, so it’s very hard to get away from all vibration.
Solutions like the Mapleshade stuff gets into tuning, which uses damping and draining where vibrational energy is focused into a narrow frequency range. In the case of Mapleshade the frequency ranges of brass and maple seem to complement each other well.
Like power conditioning, vibration control is solved on a case by case basis. Some don’t need it, some swear by it, and some swear at it. Of course if we followed my Dad’s advice and “keep that damn thing turned down and stop jumping around up there” many of these problems would go away.
