Hello menzieschen,
When trying to get triple monitor configuration, we strongly recommend not using video adapters or convertors. This is because these devices need to modify and transfer the signal coming from the system to display it in another connector type and during this process the system can be affected and therefore not displaying the information or sending the signals as it should.
At this point since you are using a DP to DVI adapter the system is recognizing the signal as Digital display and due to this will not be possible to get the triple monitor configuration.
You can use display ports or mini DP also but I am afraid that when using convertors or video adapters we cannot guarantee the correct functionality of the device.