Isolation Theory Question

I'm comparing the Vibrapod versus the Cardas/Ayre myrtle block devices for isolation in my system. My stands are Lovan Soverign with small pieces of sorbothane between the steel frame and the wooden shelves as a bit of an after-market tweak. I have not mass loaded the stands.

My question is more theoretical, as there seems to be a difference between these options, but I cannot say if one is better than the other, they are just different. So, I feel that it's pretty obvious what the vibrapods seek to accomplish, but am unsure what problem the myrtle blocks are supposed solve? It seems to me that any vibration will be transfered from the shelf to the component through the block. Is this not the case?

Right now, I seem to prefer the blocks under my solid-state amp and tube preamp and the vibrapods under my dac, transport and turntable... I'm not sure what to infer from this, but it seems that the devices that have motors prefer the vibrapods and the more stationary devices prefer the blocks. I'm curious if there is any "theory" that might help me decide what to use where?

Thanks!
-Marc