Same thing is happening to me, I suspect this is really the "Guitar In" problem. I have an HX Stomp and I loaded the same Revv Genn Purple Amp + Cab block, all default settings. In my Helix LT, it sounds clean no clipping or any distortion at all. Then I switched to my HX Stomp, and there has a nice amount of drive.
So I checked my Helix LT again and this time I plugged my guitar in the Return 1 and voila the sound had the distortion for the Revv Genn Purple. So, I looked at the settings but couldn't find anything that could possibly change the setting for the input. So, this must definitely be a hardware issue.
