Concrete Slabs

Sounds like you’ve got your turntable support reasonably well sorted. Congrats! In my experience: isolation isn’t a problem, until it’s a BIG problem. If you don’t have good enough support (combination of rigidity & mass), then footfalls and speaker energy through the floor can cause a large enough displacement (shifting the cartridge relative to platter) to excite your cartridge & tonearm’s resonance (8 - 12 Hz). This isn’t usually audible, but it can be enough to cause problems for your amp & woofers. It can even cause your amp to clip, which will send a nasty jolt to your tweeters. Absent that, it can certainly cause mis-tracking.

Concrete slab floor isn’t a complete isolation - it will transmit energy in the audible spectrum just fine - but that stuff can be handled in a number of ways, with audiophile footers or platforms. What concrete can do, is it vastly reduces the maximum displacement your cart & arm get subjected to. Because of its great mass & rigidity. Absent a concrete floor, isolating speakers and turntable are your next best bet. A properly tuned spring platform works great - Townshend podiums look interesting. SOTA’s 4-point suspension is amazing - it will absorb even large displacements QUICKLY and then dissipate the energy very SLOWLY at like 2Hz where it doesn't matter. Bigger SME’s also have very substantial elastomer suspensions, but your SME 10 appears to have a non-suspended design utilizing polymer layers.

@dogberry your system set up for your turntable is fine, enjoy your music and be grateful. Out of curiosity is there anything inside your 400lb 17th-century oak chest? If not perhaps some type of fill might be beneficial, most likely a trial-and-error experiment.

Creating a Structure to mount a sensitive item of equipment on is a Topic that will appear the more it becomes understood how the impact of the Ambient Environment on the equipment can be detrimental to it.

There is no harm trying out additional Tiers of Supporting Structure, between a TT and Table Top.

The New Addition of Materials and added levels of Isolation will bring something new to the perception of the SQ.

An assembly for a Support Structure is likely to be discovered that will surpass what is already in place.

It is the trialing of Support Materials and Isolation/Separation, that helps one determine where their objective is best served.  

Does a $4K Vibration Control Platform offer much more in control, than a well thought out structure that can be produced for a considerably less cost, or is the $4K Platform a shortcut to a Support Structure that can be mimicked using other types of Structure as a support, only Trials will assist with learning this.

As for the Oak Table a very affordable trial could be to utilise Newplast Modellers Putty. This can be used between the Oak Table Top and have a Sub Plinth Tier, seated on to it.

This as a method is now offering Two additional Materials as Tiers to create a Sub-Plinth, and can have a very valuable effect on the Damping Factor of the Structure and improve on the Dissipation of energies being transferred. 

@lak Out of curiosity is there anything inside your 400lb 17th-century oak chest?

It's a cupboard chest, so rather than a hinged lid it has two doors on the front, there is a vertical divider up the middle and a shelf on each side. One side has an Ayre C5xe on the shelf, with turntable tools underneath. The other side is full of rather disreputable LPs that would not fit on my shelves (the kind one gathers from relatives and don't like to throw out, Great Western Movie Themes, Greatest Hits of 1968, Soundtrack from Dr Zhivago - that kind of thing). Certainly adds a lot of weight. I also have a large block of wood under the chest in the centre, so that it supports the bottom where the central divider is. I'm not going to make any changes to it that would damage its worth as an antique, and I don't want to know what it's worth! I had some canny grandparents that bought up all sorts of antiques in the 1950's when the exorbitant death duties of the Attlee government meant many large houses were sold up to pay the duties when the owner died. That was the intention of a deliberate policy aimed at redistribution of wealth. My grandfather, most of his life a fitter for the Crewe railway works, had a little cash from his football career, so he bought up antiques. I can't complain!

I use concrete supports and find it a solid improvement over a wooden support and a steel frame rack.