You may destroy the sound barrier effect if you put any fasteners through your current setup. It isn't the approach I would take. You have an extremely expensive walls, make some effort to protect it.
I would build a non destructive hanging setup. You would build two ladders as tall as the room out of at least 2x4 thickness of wood. And pin them to opposing walls by putting a pair of 4x4s across the ceiling. The ladders can be any width, consider the weight of what you are hanging. And be careful not to damage the drywall when making this tight.
Bookshelves should have another vertical support pinned to the wall every 3 foot. They get heavy when full.
Then you would have a hanging system for two walls, and across the ceiling. I don't know if they still do, but college students used to do this in dorm rooms for hanging bunk beds off the ceiling. It took up less space than the free standing bunk beds. If I can find an images of the kits they used, I will post it. They haven't appeared in my searches so far.