@o_holter Are you assuming the shelves are ringing or reflecting the sound waves coming from the speakers, and adding a hardness? While that is valid, it’s not a major contributing factor. I’ve always thought of the challenge being more to do with the relationship between the supporting material and the component itself. It’s at that interface where the support-related sound quality is generated. Vibrations generated by an undamped extremely stiff material coupled by spikes, cones, or footers to the component causes that hardness. The corollary is that soft materials like cork or pine damp the vibrations and soften the sound. I’m not sure why exactly this is the case. However, assuming it is the case, the best way to ameliorate the effect is to decouple the component from the surface. I use Nobsound springs ($29 for set of 4 on Amazon) Not only does it fix the hardness, it adds dimension and speed to the music with blacker backgrounds.
Edit: It's worth an experiment and a lot less expensive than the Townshend solution mentioned above in the time I took to write this!