I used this solution to play rocket league split screen using both my monitors. Now I wanted to play with two friends so I added a third controller. This works fine until the game starts. Then you can still hear sound. From the sound I can hear that the controller input also works. Here are some pictures that might help visualisering what I mean.
I also tried starting a Exhibition match and adding the extra players after starting the match. This has the same result when the third player is added.
Best Answer
I am answering this question on request of @HazyKingdom. Please let it be known that the answer was found by reddit/youtube user vi9ke.
C:\Users\{User}\Documents
unless you have changed this yourself).C:\Users\{User}\Documents\My Games\Rocket League\TAGame\Config
.TASystemSettings.ini
so when you make a mistake you can revert your changes.TASystemSettings.ini
in your preferred text editor.This answer is tested on Windows 10.