I have been using refurbished workstations for pixinsight for a while now, and I agree - fantastic bang-for-buck.
My current workstation is a Dell T7910 which also features a dual Xeon E5-2699v3 (36 physical processors, 72 logical processors) setup, with 128GB RAM and a Quadro P4000 GPU. I also encountered the issue with only one CPU loading up (apparently a Win10 limitation), so the answer to utilise all logical cores is to use linux - which yielded a Total performance PI benchmark score of 25992.
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