The Instrument and Mic signals are summed before the gain stage (Gain Knob)
When designing the unit we didn't have room for a separate level control for the Inst In.
So we chose the current design. In a MKII version it will surely have the mic and instrument input be independent.
You can use the 1/8" AUX IN as an FX Return independent of the FX loop return jack. This AUX IN signal gets mixed into the outputs – directly
for DI/LINE and before the output level control for AMP and Headphone ). The Mix Knob has no control
on this signal. Hope this helps.