The stream studio will always start from the following location:  %LOCALAPPDATA%\Presentations2Go Controller

where %LOCALAPPDATA% is an alias for you local user settings folder.

E.g.:  C:\Users\ov\AppData\Local\Presentations2Go Controller in my case.

Here you will find the config.xml which stores the Controller settings and default.vmix, the vMix profile loaded when starting the Stream studio.

When you make changes to the vMix settings, make sure you save them in this location. Otherwise the settings will be lost when you restart the application.