RE: CSV 5300A, getting two external touchscreens working with Surface Pro 3

The MST Hub routes video streams independently to provide multiple display support. For the touchscreen I believe it has a USB interface, therefore I cannot relate this to the MST Hub.
I saw this text from a DELL service center, maybe it can help you

Issue: A customer connects a second Touch Display to a Touch based Laptop OR a Desktop already with a Touch Display.

Symptom: Touch Displays are shipped with USB Cables. When both USB cables are connected to the computer, the operating system sees two displays and two touch panels. But, not necessarily associated with the displays that they are integrated on. Hence the touch functionality may not work as designed.

Solution:
* Ensure that the Secondary Display is in Extended Mode
* To select Extended Mode, press the Windows Key + P 
* In Desktop Mode, select Charms (Windows + C), choose Settings and then Control Panel 
* Select View by Large Icons, choose Tablet PC Settings and select Setup
* Both screens will be a white background and the Primary Display will show the text:
“Touch this screen to identify it as the touchscreen”
“If this is not the Tablet PC screen, press Enter to move to the next screen.”
To close the tool, press Esc
* Touch the Primary Display once
* You will see a white screen with the following instruction:
“Press Enter to proceed to the next step to complete your configuration”
* Press Enter to synchronize touch with the Primary Display
* Touch the Secondary Display once
* You will see a white screen with the following instruction:
“Press Enter to proceed to the next step to complete your configuration”
* Press Enter to synchronize touch with the Secondary Display