better wood for a plinth

The 301 and 401's chassis are aluminum.

The Link will offer very valuable information, this is the best place to start to draw from to start to select a shortlist of Materials.

For the record, MU 25 when used on a Plinth for a DD TT and the experiences being had, were comparing MU25 to alternative wood designs, did not show MU 25 as being 'much' improved over Marine Plywood. MU 25 as a engineered wood design is the better choice in place of Marine Plywood, but falls way short when compared against some of the other available engineered wood designs.

https://forum.audiogon.com/discussions/one-turntable-with-two-arms-or-two-turntables-with-one-each-which-wo

For my SP10 I went the CLS way trying to follow the pathway of Jean Nantais. I used a core of MDF wrapped in a layer of 1/2 acrylic bonded with a flexible adhesive, then sandwiched with a Baltic birch plywood, and wrapped in a mahogany veneer. Was a very good plinth and an excellent table. One I should have kept. 

I think you mean CLD (Constrained Layer Damping), not CLS.  CLS was a great ESL made by Martin-Logan.

Mijo, The dogma would say you ought not to put any material between two layers where you want the impedance to energy sharing to be minimal. (IOW, you want to maximize the contact areas between the two materials to achieve effective CLD.) I refer to your warning to use felt between oak and metal. The felt might work to avoid staining of the steel, but it defeats the purpose of the layering.  Similarly, the old practice of using a rubber profile between TT chassis and wood plinth is now frowned upon.  Jean Nantais is among those who pointed this out.

I used Mayan Walnut for my Sony 3000 TT.

Photo in my virtual system.