I have thought about going with some shakers in the past, but every time I think about it something comes up to dissuade me into going that route. Do you run one per chair on your setup? In my setup... I am assuming I would need 4 which then makes it get expensive.
I have a pair of the shakers and amp that I have tried several times. Every time I try them it just feels strange. Like they shake at the wrong time or something... Not so bad for movies but for music its really weird. Maybe I have never adjusted them correctly. If you want to try them Ron let me know.