@unsound - no, I never paid much attention to tweaks, footers, etc.
I don't know what made me even think to put them under the Oppo. But after that, I put them under my Heed dac and they did the same thing - an added sense of harmonic richness. Taking them out made the sound flatter and more....digital? They're certainly cheap enough to try. Just make sure to use a coaster or something because those things ooze. Really.