I wanted to update the firmware on the spare PM883 I have laying around, and it looks like I might have fried it by connecting it to the PSU with a cable from another PSU (which I wasn't aware of, I just grabbed the first cable from a bag I had laying around) - it's not being recognized at all, and not even when using an USB->SATA adapter, so I guess I need to buy a spare just to be sure before I even think about upgrading anything. FML. All things considered, I might just stick with the SATA SSDs for the time being because NVMe would require me to upgrade the entire server first. Meh.
At least I do have the potential upgrade mostly thought out.