Got my Vive Pro from US yesterday, bought the plug adapters ( USA > Europe ), bought a mini display port cable ( link here ), and connected everything. Installation was very quick, and the setup itself with the linkbox is very easy.
As soon as I upgraded the HMD and the controllers I got a "Compositor not working" 400 error.
Restarted SteamVR, error gone, without unplugging the cables.
So no need to wait for an adapter or super-expensive cables in order to use the HDMI port, with the mini display port cable plugged from the linkbox into the mini display port of the MSI VR One, everything works as expected, then you just use the HDMI on the VR One for your monitor and you're good to go