Hi LeLeuPaon, 

Please be aware that for any multi monitor setup using an Eyefinity card with Mini DP outputs but NON DP monitors like the Viewsonic panels, you can connect two of the monitors with passive mDP to HDMI adapters. The remaining monitors need to be connected with active mDP to HDMI adapters since only two of the outputs on the card support Dual Mode DisplayPort (DP++) which natively convert DP to HDMI. 
For the other outputs, active adapters are required. 

Club 3D advises the CAC-1170 mDP 1.2 to HDMI 2.0 Active Adapter for the best results:  link to product page