Damn. I was hoping I'd be able to put in another stick, but then anything that populates DIMM 3/4 just makes it hang on bootup, stuck on beeping.
Nobody had or heard of this issue back in the day.
Built it & 3 or 4 other members on the forum had exact same build I went off of & they didn't have these issues.
I doubt I'll find any better answers all these years later, any more than I did back then. Shitty.