Help needed for isolation under the power amps

I need to circle back to putting the proper isolation and mass loading under my Conrad Johnson LP140 mono blocks as circumstances led to a poor resonance impasse: 

My active components (cfr my systems page) has space limitation due to the fact that they reside on two levels in the designated space of only 40"w x 28"h x 32"d within the custom made cherry cabinet that was designed for my AV needs in the mid 90s. On top of that, the cabinet has to be placed directly against the wall, which makes any change to the active components cumbersome. 

The cabinet stays (a compromise with my better half) so I can not have an audio rack where the energy drains properly to the (wooden) floor and unfortunately the European cherry of the cabinet resonates more than I would like. The "A/V equipment space" limits the use of more solid material underneath the amp (again, please see my systems page. Also note that I have Symposium Svelte shelves under the mono blocks which are not depicted as at that time when the pictures were taken as I trying them out under my other set of speakers).

Any suggestions, especially for under the mono blocks? I am going to raise the shelf a bit where the source components sits in order to put mass loading material under them. I can go as far as 4" in height.

So the question begs? Which material would you suggest? Under each amp, I could use e.g. a double stack of 16"x16"x2" pavestone, a duo of 18x12x3" granite surface plate machinist tool, may be custom cut marble slabs.   
Besides mass loading under the amps, I am thinking of adding some metal brackets between the cabinet and the back wall to offload energy as my wooden floor is a bit lively.

As for feet under the mono blocks I am currently using the BDR cones and pucks, hoping to change the frequency of the interacting resonance of the cherry wood. Am thinking to replace them with ebony footers once I have the proper mass load. Also here I solicit your suggestions for the footers.