Support table or shelf for turntable

Thanks everyone for the valued suggestions. I’ll study up in more detail all the notes kindly supplied. Thanks.
A few points to clarify:

1. Remember the new rig will (hopefully) be a rebuilt 401 in a slate plinth.
   
2. The issue I’m facing is that when I knock on the oak table legs or lower cross-member, I hear it through the speakers. I reckon if I can hear it, so to can the 401.
   
3. I want to get rid of the oak table anyway and take the LP12 out of the equation. It was a temp solution years ago and now i want to deal with it.
   
4. The granite blocks: I originally had the TT on the concrete floor on felt pads. It sounded great. I moved it to the oak table and it lost a lot - woolly and smeared. I added the 3 x granite blocks and it made the world of difference - 90% of the floor set up. I then added the steel cones pointing up and touching the underside of the plinth, and this made it sound better than the floor. This is the way it has been for a few years. Because of this experience, I feel the 401 works best when everything is as rigid as possible.
   
5. Before going the (complex) springs route, I’d really like to try something like a wall mounted table. See these brackets. Wall mounted with upward pointing spikes into say a 2" maple top plate. I’m uncertain what type of feet to add between the slate plinth and the maple. Rollerblocks?
   

I use cones  (Bearpaws) under my turntable and found it a very valuable upgrade.  Tried other things without that level of success.

The springs route isn’t all that complex, I’m more than happy to help where I can..

Placing my turnable on a spring suspended butcher block platform reduced significantly any sounds caused by hitting my rack. I really have to hit it hard to get any sound to transfer to the speakers.
If the coupling/shelf route doesn’t quite work 100%, you should definitely consider springs.
That being said, rollerblocks seem like they'd add isolation in the horizontal plane as well as isolation from torsion, which certainly wouldn't hurt.

Noromance, I hope I am not pointing out the obvious here, but the slate, by itself, won't isolate your 401/plinth from your existing table (if I'm understanding this right, not knowing if the slate will be on the top of the plinth, or under it). Isolation from the table is the key to success.

If you would, please report the outcome, for we of curious minds.

Regards,
Dan

@islandmandan Yes, I know that the slate will not isolate the table. I want to try the slate plinth as I believe that the birch-ply, while excellent at damping TT generated noise, is also responsible for a little smearing and subsequent loss of some detail. The relatively difficult, and frankly, cumbersome efforts to isolate the table can be ameliorated by wall mounting to concrete and keeping the structural hardware to a minimum.