I don't have the right words for it, but there are some important distinctions in my head between the options described above.
The most notable is a choice between high mass and low mass. Getting something that is high mass and damped is easy (ie. a telephone book). So you can get a neutral result with pleasing bass weight. But I believe the fans of this approach don't know what they are missing. If you try a Neuance shelf you will get a neutral result, but speed and detail that the high mass approach is incapable of achieving. The high mass approach can seem a good one if you are just listening to the "sound" (or harmonic structure) of instruments and voices. But if you listen to how the music lifts you up and takes you on a musical journey (some call it PRAT), there is no contest. Personally, I had all but given up on the low mass approach until I found a product that did the difficult task of achieving low mass, high rigidity, and damped across the musical spectrum. And by the way, its "sound" is wonderful in ways that you will not appreciate until you take the shelf away (isn't that right Ernie?).
The next distinction is between focussing on the shelf or the footers. As to the cones and rollerblocks out there, they provide a low mass and rigid interface, but are not well damped and so all tend to be peaky in some way. That is, they tend to channel energy into a narrow region.
The soft feet and bladders all sound distinctly odd to me in that they seem to have a region where transients are hopelessly smeered in time, more like a "suck-out" than a peak, which results in massive loss of PRAT. Some are just better than others. Vibrapods seem to be popular, but I find they add an upper midrange presence that is not welcomed by me - others clearly like it.
I guess my conclusions are that the shelf is where one should focus, not the footers. I like the E-A-R feet that are neither hard like cones or soft like Vibrapods or Sorbothane, and sound more even-handed and slightly better than rubber - but largely because they allow the Neuance shelf to just do the job without intervention from the footer.
I reckon that if you have an inappropriate rack and shelf, certain footers will sound beneficial, but will also seem like a trade-off in some way. Which is what they are. So what I am suggesting is what I found - which is that if you get a light/rigid/spiked steel rack and use a Neuance shelf (maybe there are similar products like the Torlyte shelves) you will find that the footers will sound horrible. And that is because their beneficial effects have become largely redundant and their downsides are exposed.
Apologies if this comes across like the ravings of a zealot. Just my opinion folks, but the opinion of one that is real happy about where he has got to with vibration treatment in his system.
