Not sure if someone else responded, but this is how I do it.
You can control the volume in the Global Settings ;In/Outs;USB In 1/2 Trim.... you can control the dB here, I am usually around -12dB with my Helix LT volume at 10, through headphones (and earplugs of course).
I use the same interface for my IPad Pro...works great for me.