Thoughts? Too many of them. To my mind the marbles should go with the sound activated estim as the sudden clatter of marble on metal pan should set it off nicely,  straight to his balls and or cock. I'll let you choose:)  and the ass contact to the movement sensor. I tend to think you can turn that one up more before it becomes challenging while the cock and balls react more quickly to fewer amps.
But that weight on his chest, could we not go with whatever was holding the marbles be that weight. Him keeping the "up" position as well as still would be an entertaining view.