Try to adjust
¨ FX Loop Level
“FX Loop Level” controls the outgoing signal level of the hardware effects loop for correct leveling of the external device. This helps to prevent noise or distortion. It is a global parameter and affects Loop Mono as well as Loop Stereo. Loop Distortion is not affected by “FX Loop Level”.
üIncreases of SEND output level are compensated for corresponding decreases of RETURN INPUT level and vice versa. Therefore, the level and effect loop mix of the output signal stay unaltered.
I did try to change Loop volume (when you select Loop Distortion or Loop Mono and you get Volume as the only control to the assigned effect/function) and as I described above:
Setting Loop Distortion volume below 0 makes it even worse, sounds like a dead battery or Matt Bellamy / Jack White type of fuzz (broken amp tone) and setting it above 0 just hides the tone of the pedal behind gain of the preset, totally changes it towards something like a Boss Metal Zone type of thing.
Are there any other level controls? Where should I look for them?