Yes I bet the cones direct energy into that large floor and make it sing along some.
I once constructed Platforms boxes out of Medium density fibreboard.Like a big sandbox with close fitting floating lid.It helped some,would have liked more performance for the effort.The system was in large second story room.Floor was about 14x20 no center supports underneath.I placed the speakers close to outside wall where large floor is better supported.Have you dealt with middle area where floor is prone to most movement.Picturing the barn loft must have some ground floor up supports already,can strategic ones be added?Maybe more support from ground floor under speaker locations and other loose areas.A second skin of flooring in the area of speakers or even complete platform in that part of the loft.Also club stores like Sam's ,Costco have these 6x9' area rugs made of Berber scraps,edges sewn real nice.They are about $30 each,real inexpensive stain resistant.Several can damp a resonant floor as good as the sandbox did.
I once constructed Platforms boxes out of Medium density fibreboard.Like a big sandbox with close fitting floating lid.It helped some,would have liked more performance for the effort.The system was in large second story room.Floor was about 14x20 no center supports underneath.I placed the speakers close to outside wall where large floor is better supported.Have you dealt with middle area where floor is prone to most movement.Picturing the barn loft must have some ground floor up supports already,can strategic ones be added?Maybe more support from ground floor under speaker locations and other loose areas.A second skin of flooring in the area of speakers or even complete platform in that part of the loft.Also club stores like Sam's ,Costco have these 6x9' area rugs made of Berber scraps,edges sewn real nice.They are about $30 each,real inexpensive stain resistant.Several can damp a resonant floor as good as the sandbox did.