Hello
Is not required any cable to connect the StarGo2 to the Raspberry Pi Stellarmate, you have just to connect them on the same network, then you can mange the StarGo2 Pro through KStars by using the IP address shown on the StarGo2 Pro display and the 7624 port.
So, if you are using Kstars, you have to add a profile, select the "Remote" mode, type the corresponding IP in the Host field and the 7624 value in the field port, then click on the save button.
Afterwards, you'll be able to connect to the StarGo2 by clicking on the connect button available in the KStars profile window.
Furthermore, by opening a web browser an using the same IP address, it will be possible to control the mount with the StarGo2 web app.
Attached you can find some useful screenshots.
Best regards
Stefano
Avalon Instruments Team