Pin-holes in PCBs tend to vary a bit between different PCBs. Mill-max and Holtite sockets don't fit all of them.
Not all switches' pins fit in Mill-max and and Holtite sockets.
These types of sockets tend to wear out after a number of swaps, and maybe from use as well.
The KBD8X MKII has PCB-mounted stabilisers... I'm not sure about the stability of sockets with PCB-mount stabs. Maybe someone else has tried that combo?
BTW, "top-mounted plate" means that the plate is bolted into the top part of the keyboard case, as opposed to the bottom part or both.
The PCB is supposed to hang from the switches' solder joints. You might have to disassemble the case and lift out the plate-PCB sandwich and place it onto a towel/foam/whatever whenever you are swapping switches.