You need to map all streams, so
ffmpeg -video_size 1920x1080 -framerate 60
-f x11grab -i :0.0
-f pulse -i default
-f openal -i "Monitor of Headset H390 Analog Stereo"
-map 0 -map 1 -map 2
-c:v libx264rgb -crf 0 -preset ultrafast video.mkv
See http://ffmpeg.org/ffmpeg.html#Stream-selection for how ffmpeg automatically selects streams when map is absent.
I always avoid excess tracks. You can add as many or few tracks of each types as you want in "Add Tracks..." Simply adjust the number of tracks to be added by clicking on the number. It defaults to 1 video and 1 audio track, but that can easily be changed each time you add tracks.
You can also add an individual track to either by right clicking in the ...
Add your video to your timeline. Then you play the video from the beginning. Now you are going to insert a marker every time you want a new clip to be inserted. If you have CS6, the shortcut is M, otherwise it's * on the numpad.
When you've added all the markers, you should delete the video track (since you only want the audio. If you want to render the ...