I'd recommend you save headaches, money and complexity, return the Scarlett Solo, and get this or something similar (since you clearly have an appreciation for used gear):

https://www.guitarcenter.com/Used/Roland/UA22-DUO-CAPTURE-EX-Audio-Interface-114485698.gc

USB-powered with two inputs that can accommodate line/instrument/mic-level signals plus MIDI I/O.

Just add cables.