PSU make and model?
I would have liked a bit more of the dump file just under the part you posted, but not beyond the place where you get just a series of jibberish that only a true PC geek could interpret (i.e, the stuff that no longer is in English).
But I would ask, is the BIOS up to date
Are the chipset drivers up to date?
.... [edit: incorrect product link removed]
Is .NET Framework 4
installed along with updates? [Should have been included with the driver install.]
Did you attach the crossfire cable?
Is Win8.1 up to date as a hotfix may exist for your problem?
Did you reset any overclock to defaults before the install?
I would run memtest86 (v4) or memtest86+ (v5) to bolster a defense it is not your memory. In fact, what is the exact model or provide a link to your RAM.
You are using the two PCI Express 3.0 x16 slots and not the PCI Express 2.0 x16 slot?
The current Catalyst drive is the same as the driver on ASUS support site. You could try the latest beta driver
You have done a fine job of demonstrating the crossfiring itself is likely the problem (provided you ran a single card in each of the two v.3 x16 slots). The only two things I can think of at this point is to do a CMOS reset per your MB instructions, with both cards installed before you boot.
The other is to uninstall the video driver
. Reboot with only one card installed and reinstall the latest
or beta driver (I'd try both ways). You should run Windows Update to make sure any associated apps loaded with the driver don't have fixes needing to be installed to bring everything up to date. Then shutdown after it proves stable and install second card.Troubleshooting Lower Than Expected Performance, Crashes, and Hangs in Games
Please keep in mind that you are on the fringe: Top of the line PC, OS and now demanding two high end GPU cards communicate with each other. When you do new you are the one on the frontier dealing with the issues. But you are not alone.
I would suggest opening up a tech ticket with ASUS TS. I suspect they will be interested.