Optimal I/O settings for recording QC into DAW

I am attempting to do a comparison of amps from processor to processor (Quad Cortex, AxeFXIII, Kemper, Helix). I will compare the AC30, Marshall JTM 45 and Fender Super Reverb examples from each unit. I started off using Studio One Pro 5.5 and had some issues so I switched over to Reaper to see if it makes a difference.

My question is, what are the optimal settings for I/O so that I can get a proper recording level into the DAW. At first I was getting a very low level. With some research I was able to learn how to tweak the levels but now it’s distorting my signal. Any additional tips will be appreciated as well. It’s been a very long time since I’ve tried anything like this so please go easy on me :upside_down_face:

Neural recommends that the best SNR is achieved by keeping the big volume at 100% and tweak your presets/signal chains as needed. I keep everything at or slightly above unity as much as possible.