Sand boxes are great for adding mass to a turntable, or to an overall shelf/rack, and that helps with isolation, to a degree. But it will not stop everything. In fact, the mass on a sandbox actually couples to the stand and some low thumping vibrations (i.e. knucke raps on the stand itself) will still be transmitted through the turntable. The Ginko solution will in fact get rid of these.
Coupling a Ginko type solution to a sandbox will get you 98% of the way there. Here's my stand - integrated sandbox for each shelf w 50 lbs of sand in each, and a DIY Ginko under the turntable using 12 squash balls under a 1" maple butcher block sitting on top of the sandbox shelf.