Set up for 4CM in Helix Posted October 13, 2017 This will depend on the Input Sensitivity of your Guitar Amp's FX Loop. Try Helix's Settings both ways. You won't damage your guitar amp. It will just be louder or lower. Go with the setting that is closer to when you are using your amp directly. According to the Quick Start guide I should be setting it to Instrument, but using the 4 cable method it sounds much louder (better?) in Line. I'll play around a bit and maybe there is a benefit to Instrument, but initially it sounded like Line was the way to go.