Input and output are interesting in a tiny rack like this. For output, I chose to lean on using one of the Maths attenuators as your output (you'd need a 3.5mm to 1/8" cable, I think this would work from prior comments by @lugia) or would suggest an external mixer. For input, I think you'd want to sneak in a dedicated module, for example the Mutable Instruments Ears. I don't process external sources though, so I'm not an expert on that one.

Glad this has been helpful, others may chime in too but either way keep us updated on your journey!