I've messed around with CD player isolation for a good number of years now and feel that it's actually more important to drain vibration away from it rather than isolate it from the outside world. To that end I've not been over impressed with sandboxes, inner tube related things or sorbothane.
Best cheap tweak I know is pumice stone - three of those little pear shaped things for your feet.
Best isolation tweak I've heard - by miles - is a device made from three layers of phenolic resin with hard alloy concavities and ceramic bearings captive in the alloy dishes. It allows the player to gently wobble for about 5-7 seconds after you push it.