Flattening a sophisticated dedicated packing is often impossible. Where it is possible it will certainly reduce the integrity of its structure and invalidate any warranty given by the manufacturer, thus probably negating the benefits of having retained it.
I am fortunate to have ample attic space, but the problem is that boxes for big kit do not fit through the entrance door. I keep the wooden crates for my Krell KRS200s in the gargen shed. They have moved with me through three homes. Where you have no space to store this is indeed a big problem. Being unable to create space, I cannot assist.