Thanks a bunch. Is it possible I can find this stuff locally at Home Depot/etc?
I dynamatted my car trunk a long time ago when installing a subwoofer (helped a lot with minimizing rattles).
If I can find all this stuff locally I'll definitely take care of it this weekend. There is a furnace cold air return in the basement also, would be great to quiet it down since the theaters are next to it.
I read not to block the return really or it'll "suffocate" the furnace, but it probably means don't completely block it, a potted plant might work.