The signal flow you’ve described sounds correct. As to whether or not the operating levels on the H90 should be set to instrument or line, I am going to guess “instrument” levels, since that’s what properly modeled amps are expecting at the input – an instrument-level signal. However, the post effects path (QC insert 2) will depend on where the QC is connected to. If you’re connecting it to an interface or a FOH mixer, perhaps it may be better to set the H90’s output to line level. Experiment to see what sounds best. To be sure the H90 operating level is set properly, you should not be hearing any volume jumps when you activate the H90 in the signal path.