I could go on an endless tangent of expletives at my computer but I am just... tired
Well, this has been a whole buildup to nothing. Turns out the problem I'm running into is rooted in the CPU, and there's... nothing I can really do except replace half my computer .-.
Does anyone have any recommendations for Ryzen hardware that I could pursue? Gonna need a decent CPU and a motherboard with dual 16x slots + proper IOMMU isolation between them. 
...Ryzen is still the current AMD architecture, right? ;;;;
@elfi yes, it's still ryzen.
Unfortunately, they're in high demand right now because everyone is quarantined and building gaming PCs.
@k heckie
I've been getting by on an i7-4790k but my attempts to virtualize while dealing with my IGP (memory IO bottlenecking, DMAR faults) keep running into issues, up to and including that my entire PCI-Express expansion bus is tied to a CPU and thus I can't even put a separate discrete video card between my host and guest without ACS overrides, which my tests have discovered lead to astonishing amounts of video memory corruption!
@k I don't know what the market is like, whether midrange stuff is still on the table or not, because I don't need a LOT... Just something that isn't a complete disaster with ACS, which is to say not an Intel system