Stereo Tool

So first I start qjackctl, then I start Stereo Tool. But how to configure Stereo Tool so that it receives audio that is now playing, process it and then outputs it through the speakers or headphones? When I set input to monitor_1 and monitor_2, it doesn't work, but it works when I set it to capture, which processes microphone audio. I need help.

I FOUND THE SOLUTION!!!!
According to this tutorial: https://www.youtube.com/watch?v=UVhRDU6Kcds, I followed steps:
1. I installed pulseaudio-module-jack
2. I setup scripts in qjackctl according to the tutorial video
3. In Ubuntu sound settings I chose the Jack sink for the output device
Now the normal sounds (e.g. YouTube videos) are playing when Jack is running.
So I'm now starting Stereo Tool.
In Input I choose the PulseAudio JACK Sink (left and right are front left and front right).
In Normal Output I choose system:playback_1 and system:playback_2
Now when I play for example a YT video I have echo. I solve this by disconnecting the Jack sink from system in qjackctl.
And I solved the problem! The only problem is that my laptop is too slow to play a YT video and run Stereo tool at the same time without stuttering, but it's for another thread.