I have had a look at the link offered by @oldrooney
The offer of the individual posts is a option that allows for creativity.
The Cross Brace Legs, can be found at 13" Shelve spacings, @ 80lb capacity per shelve, if the Vinyl LP storage option is looked at.
The description given suggests this is a stackable system, with a guidance up to 42" in shelve height @ 240lb capacity per rack. I have not been able to see how these racks use fastenings to couple together, maybe it is not a fastened together assembly when modules are added.
Additionally, the Amp Stand has an 'X' Brace option, if this was the Base wanted for the Rack, it would need to be made known if this is compatible with the add on system, as no images show this base as the base on a assembled rack.
As for the creativity, the Width Spacings between support posts, can be bespoke chosen, if ones own board material is chosen. As there will be potentially 4 x posts required to be purchased, this opens up the option to extend the rack to a Three x Cell per tier system. If one wants the Shelve/Sub Plinth to be produced from the most attractive material (performance wise only), the suggestion of a Phenolic Resin Impregnated Densified Wood Board to be used, has real merit. This as a material will not be bettered at the price it can be found.
Do bear in mind their are businesses now set up around offering Panzerholz as a Sub Plinth material and some are asking approx' £1000 for a board with a dimension 500mm x 400mm x 25mm.
Linn are now following Clear Audio and are using a similar type material on their £50K+ New Model TT.
There are also TOTR Speaker Manufacturers using this material to produce their cabinets.
https://www.audioadvisor.com/furniture/furniture-accessories/?page=2