[Obsidian Dragon]

I haven't done this but my understanding is that the output from you interface (Scarlet 4i4) is line level. The wah pedal operates at instrument level as does a guitar plugged into an input. The preamp on the input can compensate for the difference in levels so that you can record instrument level into the track. The problem I see is that a line level signal coming out of your interface is not adequate to drive the wah pedal's input. Wah pedal inputs are finicky in that they interact with the load from the guitar's pickups. Since you interfaces output will not have the similar pickup loading, the wah will not respond as desired. Often to do this type of setup (out from the interface for instrument level processing and back into the interface) you would need a reamp type device. Radial makes some devices specifically for this purpose. I hope this helps.