In windows 10 do the following as a starting point...
1. Increase page file size to at least 16GB
2. Change power profile to high performance
3. Set afterburner tdp to 65-70%, default clocks, once stable then +100 core, +500 mem as a starting point after crashes are stopped
4. Report back the cpu usage when mining 2 cards then all cards, +cpu specs please, what is it?
5. Pcie power cable from PS to cards and riser should be on the same 12v rail.  If you use 12v rail 1 for all risers then other rails for cards it can possibly create problems.  Not sure if your PS has a single or multiple rails.
6. Bad power wiring...never exceed 300w per pcie cable is my rule of thumb.  I typically use a single pcie power cable for each riser + gpu using a splitter.  I use server PSU's so all wiring is pcie cables.  Please ensure your loads are balanced and proper, not some BS like all risers on one cable.

My thoughts of why the crash...
1. If you didn't turn down the tdp in afterburner you might be causing issues on the PS.  Did you split the loads across each 12v rail?
2. Virtual memory/page file size does help and is necessary
3. If the cpu is a terd it will certainly choke throughput, but shouldn't crash
4. Possible bad pcie power plug.  I had a burnt plug on one of my 13 gpu rigs.  Slightly burnt and melted causing all kinds of havoc.

I suspect tdp + page file combination causing issues.  If your power wiring is jacked, another real possibility.

Are your pcie x1 cards touching each other at the mb? Slide a piece of paper between them for a test.

A photo of the rig wiring  would help.