A reappearance of Black Diamond Racing?

Well if you are building a plinth, I really don't think you can do any better than a BDR Source Shelf. Even the thinner Shelf would be better than pretty much anything else you could find. I built a few and nothing came even close to the Source Shelf. The stuff is just so damn stiff and dense and highly damped- perfect for a plinth!

Don't be put off by it being carbon fiber. There is really only one layer of carbon fiber on each side. As far as cutting, shaping, machining, sanding, polishing, it works just like wood. Very, very hard wood. Not as hard as aluminum. But I have some very dense hardwood in my shop that is actually harder to cut and sand. Very doable.

Mine was cut first on a band saw, then hand sanded. Other parts were routered, drilled, and cut and threaded just like any other material. 

If you decide to try it first wrap the whole Shelf in blue painters tape. Leave the tape in place all the way to the end. That way only the areas you work get exposed and you wind up with a perfect blemish-free finish.

I just unpacked a couple of Torlyte shelves I bought back in the 80's or early-90's. I'm going to try one under my Townshend Rock Elite table, to see if Torlyte is still a contender. VERY low mass, high stiffness-to-mass ratio, but made of wood (fabricated into a honeycomb structure). Torlyte was popular when the Linn Sondek ruled the world.

I still have a couple of Torlyte products from back in the day.

Russ Andrews is a...interesting gentleman.

Torlyte was the talk of the town 30 years ago.  You don't hear much about it now?

@millercarbon,
Thanks for the tips!

Ideally slaw you would find a used Shelf, or two, or even better a Source Shelf. If you are unsure a simple proof of concept will remove all doubt. Simply drill a hole or two to mount a bearing, add arm and motor, see how it sounds. I bet even without being careful, just slapping a motor on, piece of wood or MDF for the arm board, hardly even trying you will still be hearing a deep dark noise floor and more inner detail than ever. I mean it just kills it in terms of dropping the noise floor. 

This way if for any reason you don't want to go on well you still have a Shelf only with a hole in it but still perfectly good for sitting components on. But that won't happen. You will want to go on.

If you look at mine one of the top images shows the Miller Carbon sitting on a Source Shelf. https://www.theanalogdept.com/c_miller.htm The table itself was all built from one Source Shelf. The plinth was cut out of a Shelf much like it looks in the photo. The left corner was then cut into a 5" diameter circle to be used for the nut that screws onto the bearing. Scroll down the page to a side view to see this. The right corner was cut into a smaller 3" circle to make the tone arm mount. Those Things and Cones thread right into the plinth. 

This is all based on a modification of Chris Brady's Teres turntable. http://www.teresaudio.com/fame/index.html Chris no longer makes the tables but he used an arm board so you could run virtually any length arm. https://www.usaudiomart.com/details/649452242-teres-255-baltic-birch-turntable-with-signature-motor-... Mine goes for maximum strength and stability by making the sides more curved and using a solid arm base instead of the board. Either way works fine it just depends on what you want.

Every time I go back to that site it reminds me how long I've had my table. More than 16 years now!