1-1. The DP/SS MUX is used for multiplexing between the USB 3.0 and DP lines based on the selected alternate mode configuration. The DP Multi-Stream Hub is used to split the DP lines into multiple streams so that one could be used as DP output while the other could be used as HDMI output. For part numbers, please refer to the CCG4 based Dock design which uses PS8742B and STDP4320 respectively.
2. Yes, the firmware can support alternate mode but needs to be enabled and configured in the PD controller project of HX3PD. Please find the firmware source with the Dock SDK.
3-1. Yes, those PDOs are enabled by default in the HX3PD firmware.
3-2.The customer can change the same using the DMC .xml file in the HX3PD Configuration Utility. Please refer to section 3.2.1 of the utility guide.