emplying devices under or on top of a component, is a form of tuning, like a tone control. since no stereo system is perfect, hard or soft objects will affect the frequency response. i would conjecture that the choice to absorb or drain is subject to personal taste.
i prefer soft objects, because i find that usuually, hard materials, "harden" the sound.
i prefer soft objects, because i find that usuually, hard materials, "harden" the sound.