You don't need CNC, unless you yourself make it a requirement. What you need to eliminate footfall problems is a two stage approach. First stage, mass eliminates large amplitude low frequency footfall type vibrations. Second stage, springs isolate the turntable from the smaller amplitude higher frequencies that get past the mass.
With a superior product like Townshend Pods your table will probably be fine even with your existing rack. People who have PM'd me about problems like this tried Pods and they work great in situations much like yours. They work even better in situations like mine, which is why it is still a good idea for you to build a sturdy low profile rack with a massive sand bed. As described above.
You really should as a general principle ask the question you want answered. You came here asking about metal when really it is about footfall problems with your turntable. At least that is what it seems to be. Until it changes yet again....?
