Try using an ACTIVE adapter cable, not a passive. Also, if you can run it via HDMI-HDMI or Display Port to Display port. I have two monitors running at once, one is HDMI-HDMI, and the other is Display Port-Display Port and I have no issues.
Did you ever get this sorted out? I have the same card and I get no video from any of the ports once I install the AMD drivers in Windows 10