Thank you so much for your insight. It indeed seems very likely that the SMBUS address overlaps with the RAM given the POST code and the comments in the link that @cageek posted. I've tried multiple variations (single/double sticks, slot A/B, various sizes, different brands, etc) but I keep getting the same POST code.If it helps, the memory sticks have smbus addresses too (where their memory timing profiles and sometimes RGB controllers are accessed). Given both of us saw the white/amber blink pattern give a memory POST code, maybe different sticks of ram may work? Only bother trying this if you already have other ddr4 sodimms, obviously, since this is just a bad idea that I have.
I've updated the NIC using Intel's BootUtil to 27.3, but this only updates the Option ROM and not the actual firmware? (And also didn't help with the POST code.) Would it make sense to try and update the firmware using the updater from Dell? I'd like to see if this can be fixed with firmware updates or cross-flash to stock Intel before resorting to the 'tape the PCIe pins' method...