Add audio sources in the Sources pane of studio. If it's a microphone, it'll be an Audio Input source. Just choose the appropriate device. If you're capturing the default output, or the Soundflower virtual device, then add it as an Audio Output source. Right click on each source to rename it, if you find that helpful.
(The restriction of one input and one output device only applies to what you set as the defaults in the Sound control panel; OBS as well as chat programs like Mumble really don't care what you have set there unless you try and use the Default device setting. Avoid it. All you need to do in the Sound control panel is set the default output to SoundFlower so you can isolate the game audio; it is also helpful to disable all other sounds like OS alerts, or divert those to another device.)
You can then assign each a different track in the Mixer by clicking the gear icon in the Mixer section.
In Settings > Output > Recording, choose Advanced Output Mode.
In Recording format, choose a container format that allows multiple audio tracks, like mkv or mp4. MKV has the advantage that if an error occurs you can recover a partial file. If OBS crashes or your disk fills while recording an mp4, forget it, it's all gone. After recording remux your mkv into an mp4 with something like remux or handbrake or mkvtools. You'll be able to import this file into an editor and you'll have multiple independent audio tracks.
What you won't be able to do with this setup is hear your game. Use the free LineIn program to forward audio from your SoundFlower device to a pair of headphones or a set of speakers so you can monitor your game while you play and record.
https://rogueamoeba.com/freebies/
