I have had Simaudio I-3se, I-5, and I-7. The Sim pucks are the way to go. They are about the size of a nickel with a leather like cushion on the bottom to protect any shelf they may be sitting on. In the event you don't want to pay the Sim price or wait for shipping you can easily take four nickels, cut circular pads from an old piece of leather, and glue to the nickles. Whatever you decide, enjoy the amp.
