Hi Andy :
Two monitors on VGA and HDMI :
Booting windows : two screens are up
Coming to logon screen : hdmi go to sleep mode. VGA is fine.
Disabling then Enabling the HD4600 in device manager : hdmi is back.
I don't have any DVI monitor available at this moment.
I've try the devcon script but while i've set the good pci/vend argument, the message is "device not found"... I'm doing that manually now. I'll add a discrete GPU as a workaround...