Uable to install crimson relive 17.9.2. on Windows10 with Dell UP2715K

After multi GPU finally making its way back on the newest Radeon, I've problems with the latest 17.9.2 drivers to function with my monitor, a Dell UP2715K on two displayports (mst).

After the installation the screen stays black, out of synch. and the pc reboots itself with only a lower res. and with one GPU disabled in devicemanager.  Enabling back causes the same black screen again. Radeon settings mentions there is no screen connected with AMD products, also no mention of crossfire/multi-GPU.

 

Some specs:

W10 fresh install

crimson relive 17.9.2. (without relive)

2x RX Vega 64 Liquid (Powercolor)

CPU=6850K

Mobo Gigabyte Designare X99, bios F4 (latest)

Dell UP2715K, on mst with two displayports.

 

One note, the system worked just fine with windows 7 in multi-GPU, so the GPU's aren't defective.