The TBT-6950PD docking station can drive up to a maximum of four external displays using a combination of two different technologies.  

The dock provides two HDMI video outputs, labelled ‘HDMI 1’ and ‘HDMI 2’. The two HDMI outputs are driven by a DisplayLink DL-6950 chipset. DisplayLink technology is compatible with almost all modern Windows and macOS computers. The result is that both HDMI outputs will function so long as the required DisplayLink software is installed on the host computer.

The dock also provides three 'downstream' Thunderbolt/USB-C ports labelled with the Thunderbolt logo (which looks like a lightning bolt). These ports are driven by the Intel Goshen Ridge Thunderbolt chipset. The capability of these ports in regard to video output is ultimately determined by the capabilities of the host computer.  

When using a host computer that supports two external displays via Thunderbolt, it will be possible to connect up to two additional displays to the dock's downstream Thunderbolt ports by using either USB Type-C cables or USB Type-C to video adapters.

When using a host computer that supports one external display via Thunderbolt or USB Type-C, it will be possible to connect one additional display to the dock's downstream Thunderbolt ports by using either a USB Type-C cable or a USB Type-C to video adapter.

NOTE - It is NOT possible to connect three external displays to the TBT-6950PD via the Thunderbolt/USB-C ports. The maximum number of displays that can be connected via the Thunderbolt/USB-C ports is two.