Well, I managed to quiet down my Sakura pachinko. I bought some 1/8" closed-cell foam and put strips and squares of it in areas of the machine where balls fall onto plastic. I wasn't able to hit every area due to some tight tolerances, but as it stands now the machine is a lot quieter. I got 1/2" closed-cell foam to go into the ball tray as well. It sure makes a difference. A little "thud" instead of a loud "whack."

Now I'm just waiting for my volume knobs to come and I should be good to go.