Do you have a link to manual for it that would also have mb layout / architecture?
There is a reason to have 12 slots, but I am not really sure what. Those CPUs are 4 channel RAM, so should have 4 or 8 DIMMs per CPU. I don’t know what 6 DIMMs means, so that could be crippling. Still, for MM (or any other plotter), you want to have all DIMMs populated.
Also, based on what I found is that it takes RAM up to 1,600 MHz, but doesn’t say in that doc what type (e.g., LRDIMM, …). Although, that page has max at 96 GB RAM what is also odd.
That 95W is just a paper number. Once you push that CPU, my take is that it will easily draw 150W if not more (given the heatsink will remove that heat to prevent temp throttling). If you will not vent out that heat to the side, it will bring RAM, and everything else around by few deg up, so throttling may happen on any component.
The fact that the box runs cool implies that it is not really pushed much, or it is throttling a lot.
My suggestion would be to try with just 1 CPU, but most likely it will just see half of your RAM, so that would be SOL.
To run 2 MM instances, you will need to have at least 256 GB RAM (2x 110-115 GB per MM instance). So, you are SOL here as well.
I would really clean that box nicely, sell it and purchase another similar box that takes 256/512 GB RAM and the same gen CPU (e.g., that z420, or Dell t7610). If you step up to v4, you can get potentially big speed improvement, but at much higher cost, so may not be worth it.
A couple of options to try would be to try BB Disk (in my case, it is much slower than MM, at least on dual v2 CPUs running Ubuntu). Another to use Win, and something like Primo Cache to front t2 folders. In both cases, upgrading your RAM to max would be helpful (again, I couldn’t make MM work in Win on my box, as it was 4-6x slower with 2 CPUs than with just one installed). Although, that money potentially can be better spent on that other box.