When you say "... I seem to prefer", you said everything. As for looking to vibration theory for guidance, I have yet to see any vibration mfr, reviewer or dealer put forth a reason for why one strategy is better than others and back it up by applying the complex mathematical and physical models for even just one audio system with room structural and acoustical interaction.
In my system, I found that brass cones under the DAC makes a positive improvement. The tubed amp and prea-amps, the stock feet work best, cones do not make a difference and rubber makes it worse. Under the transport, the stock feet again work best. Speakers worked better with the included spikes on carpet, worse with the spikes on hardwood. Don't know why it is so, don't care. All are very slight differences with the exception of my one-time Digital Lens which saw a vast improvement with a brick on top - it stopped the xfmr induced humming. (Something to be said for mass loading theory, I guess). Trying to predict all that ahead of time with theory would have been futile, in my opinion.
Trial and error with an open ear - that's the surest bet for your particular setup and environment.
In my system, I found that brass cones under the DAC makes a positive improvement. The tubed amp and prea-amps, the stock feet work best, cones do not make a difference and rubber makes it worse. Under the transport, the stock feet again work best. Speakers worked better with the included spikes on carpet, worse with the spikes on hardwood. Don't know why it is so, don't care. All are very slight differences with the exception of my one-time Digital Lens which saw a vast improvement with a brick on top - it stopped the xfmr induced humming. (Something to be said for mass loading theory, I guess). Trying to predict all that ahead of time with theory would have been futile, in my opinion.
Trial and error with an open ear - that's the surest bet for your particular setup and environment.