I got a FocusRite Scarlett as well. Unfortunately, I'm not in front of the computer that uses it as I write this but from what I remember...
Download and update to the current ASIO driver.
Then, make sure your OBS Studio audio sample rate is the same as the audio format property set in Windows Sound.
In Windows Sound:
- Playback = FocusRite Scarlett USB, set default device; make sure audio format property is set to 48khz
- Recording = FocusRite Scarlett USB, set default device; make sure audio format property is set to 48khz
- Disable other audio devices from their ready state you don't need
In OBS Studio:
- Setup audio sample rate to 48khz to align with the Windows Sound settings
- Scene source: Audio input source FocusRite Scarlett USB
- Scene source: Audio output source FocusRite Scarlett USB
- Monitoring device set to FocusRite Scarlett USB in Advanced Settings
- Mute the webcam mic to avoid being recorded
Play with the Audio Monitoring dropdowns in the Advance Audio Properties to determine what audio device flows to your headphone monitors and which go to what tracks to be recorded (Output).