I think its less important than the source impedance. To be honest I need to do more testing to confirm the effects of the input impedance of the next device. Preliminary testing suggested it was negligible. The technical data provided by Focusrite for the Scarlett indicates the line input is 10K Ohms, but it does not specify the instrument input impedance for the built in DI. I can only assume the two are the same in this case. The price point also lends to this assumption. If that is true, I highly recommend using an external DI box into the mic input. The results will align more with your expectations. Regardless, I think you’ll appreciate the sound of a good DI anyway.