Inside a DAC, on of my favorite topics.
Back long ago in a small column of comments from Europe, A fellow mentioned stuffing digital gear with antistatic foam.
I read it at the time and promptly stuffed my DAC. Better sound, forever.
Anyway I STILL use another better version of that brand of DAC stuffed with foam.
The main thing is keeping the conductive material insulated. As for heat, the DAC is no warmer than before. and is on 24/7
I suppose one COULD use crystals for the same effect. To soak up the stray RFI from the chips, and reducing internal digital grunge.
Even if a stone is not fully conductive, I would keep it OFF live signal lines to be safe. Even a thin piece of Teflon plumbers tape. Or a bit of packing tape stuck to the underside of the stone...