Hi cracker666,
I've been following your problem with the 3 x Pro Duo with interest as I have 4 x Pro Duo's on the way!
I was hoping to put them in a single rig!

I have a few questions / suggestions:

1) Are you still using the same Z170A XPOWER GAMING TITANIUM EDITION motherboard?

2) Are you using the latest version of EthOS (1.2.0 released 3 days ago)?
I note that this includes an update to latest consumer card AMDGPU 16.60 linux drivers which don't appear to support Pro Duo.
AMD site shows only workstation linux drivers as supporting Pro Duo http://support.amd.com/en-us/download/workstation/previous/detail?os=Linux+x86_64&rev=15.302.2001

3) Have you tried the latest version of Pro Duo Windows Drivers (17.3.2 released 4 days ago)

Good luck!
I'm hoping there is a solution.