All -
After spending a few days with the Opus in my rig, I noticed significant processing hiss, even with everything bypassed (essential a blank preset). After troubleshooting my overly complicated pedalboard, I isolated it specifically to the Opus in the FX loop. Could not figure out any other way to eliminate it- on a lark, instead of connected the 1/4 line out to amp FX return, I switched it to the "to speaker" 1/4 jack, changed the switch to line level from instrument (after experimenting with both) and presto, all hiss gone!
If I understand the manual, that "speaker" jack is passing completely unprocessed dry signal back to my amp & cab for use live, which is what I want. The Opus is still putting out the fully processed signal via XLR as desired at usable level into 3rd Gen FocusRite 8i6 into Reaper. The input level meter on the Opus barely registers, but after 2 or 3 days of recording clips and A-B comparing, I'm pretty happy with the results.