All Max/MOH or any similar sized headphone amp, go to local home improvement store and get some some 3/8 cap nuts. The top looks like a round dome, place these under amp with the round top against amp bottom. You will be suprised at the increased detail without sounding bright, total cost will be $1-2.
I usually use these under smaller components that I can't easily use bearing isolation devices, trust me this works.
Wouldn't the amp slide off the caps if the rack/table/etc were to shake a little bit?
You have to use your own judgement, as individual set-ups/conditions may vary. Use 3 capnuts and place them 1/2" in from the sides, nudge your unit to see how easily it slides and then make your own judgement. If it slides too easily you may not want to use, depends on weight of unit and surface texture of amp bottom.
You could buy three cheap small cones, and point them up but even cheap cones cost @$10 each, and will sound a little different
than round cap nut.