I answered a PM from respected_net on another forum but thought I’d share it here as well...
I too have granite shelves on my rack with a Lampi Atlantic Plus. This A+ came with some custom metal footers attached to the chassis. The metal footers were not playing well with the granite shelf (makes sense), so I put a layer of Herbie’s Audio Labs Grungebuster Dots between the two surfaces. I thought this was good, as it relieved the issue...but over time realized I was missing some highs and details.
Once I had freed up a set of DiDs I placed them under the Lampi and ‘boom’! Detail, smoothness and delicacy abound. Very nice.
Turns out the rubbery Grungebuster layer was preventing inner chassis micro vibrations from draining out of the unit (again, makes sense).
Sure, the Iso-Pucks are great for the price —i have them under my amp and my power conditioner but the DiDs are doing great under the DAC letting all the detail through.