I'm not sure if you ever figured this out, but I just got my 2x Pro Dou's set up in quadfire. So far everything seems to be working, all GPU's are recognized. I initially had trouble getting the drivers to install, so I performed a cleanup with DDU and reinstalled which seemed to fix the issue. I hope you were able to figure this out.
Also, I wanted to see what type of power supply you're using. I have a 1300w Antec, but it seems to be unstable when I hit around 1200w...I'm in the process of RMA'ing the PSU in hopes that it will fix the issue, but I may need to upgrade if that doesn't work. Just curious if you've found a reliable one?
Did you figure out your problem and did you fix it ?
I have the same problem will two Asus ARES III
I have the same problem, drivers after 17.9.3, you can only enable 3 gpus. 4 gpus in crossfire do not work.
I have 2 ARES II as well. This is clearly a driver bug
Have an issue that is similar to your's but with Radeon Pro Duo Polaris. Did you manage to fix it?