I tried changing those settings in the bios to no effect. Both in Win 10 and Pro. Still get the BSoD (atikmpag.sys)
Though I have to note that in Win 10 (not Pro) it was able to update the driver for the 5th gpu without touching the bios. It went to BSoD (atikmpag.sys) when trying to install the 6th. Where as in Pro I didn't even get past the 5th before reaching BSoD (atikmpag.sys). So I guess that's progress. When should I use 6xGPU_mod, after installing Win 10 with one gpu plugged in and not updated the driver?
Update 10/28/16: I have now been able to boot into windows 10 with all 3 gpus using crimson 15.12. But the 3rd 295 is not recognized. And after a few min of being connected to the internet I get BSoD, lol. Oddly enough if I disconnect from the internet its all good. I'll try and upload an image of what 6xGPU_mod wrote later today (I did not apply its settings yet cause I wanted your feedback of it).