got a XFX Merc 319 16GB 6800 XT working with my 16" MBP
Based on the nice tips from all over this site, I was able to get a XFX Merc 319 16GB 6800 XT working with my MacBook Pro 16 (2020/internal AMD 5600M). After a few tries, similar to the ones described by iStage, I got it working. The GPU is huge so i have a Razer X case semi open to use it. Best yet, I was able to mount, at the same time, into another port, A MSI Nvidia GTX 1080 Ti. Now it's a killer machine to use with Agisoft Metashape (which was my main objective). Sometimes, to get them mount correctly, I have to disconnect and connect them a couple of times. Contrary to iStage, I did not had to deactivate any thunderbolt root port. As a matter of fact I'm using the top one from the left side to the AMD 6800 XT and the top right one to the Nvidia GTX 1080 Ti.
The main tips are:
Use Windows 10 1903 V1
Turn off Safe boot in Mac and SIP
Very important!!! Use the modified efi from here: ( https://egpu.io/forums/bootcamp/macbook-pro-16-windows-egpu-error-12-fix/) - for me this was the crucial step.
After install the drives from Bootcampdrives (i've installed the latest RED ones)
If you want to use also a Nvidia, start with it connected and recognized by the EFI to be able to install the drives for it. In my case I'm using a Sonnet Box.
The machine it's a beast now. I can use simultaneously the two eGPU's and the dGPU (AMD 5600M) at the same time in Agisoft!!!
Thank you for your post. Pls consider submitting a build by completing the build template to give more RDNA2 goodness.
@nando4, I'll try to post using the template as soon as I turn the process more predictable. Sometimes I startup and I have a black screen. If I startup again I got the screen back after the login. Now I've found that If I startup with the eGPU already connected, touch a key during the EFI test, disconnect the eGPU until the login seems to be the right choice. Somehow the system starts differently if the eGPU is already connected. After the login I connect it to the right side, disconnect and connect it again in the left side and this seems to be working all the time. It's a little bit strange but it works. If I do not connect and disconnect in opposite ports, I only get the Audio and PCI mounted, no VGA. To have it mounted in a predictable way I have to do the exact sequence I described. The same must be made with 2 eGPU's. In this case I start with both eGPU's connected and disconnect before the login. I connect them after the login with the Nvidia in the left side and the AMD in the right side. After I disconnect both and change their ports with each other and all eGPU's are mounted correctly.