Whatever you do, make sure you set the clean sens correctly before touching any volumes, be mindful that browse mode and performance mode may have different clean sens settings, the input section can be locked or left unlocked and therefore different per Rig. I'm a use-one-guitar a performance guy, so I keep the input section locked and set clean sens for the guitar I'm using that day. The clean sens is adjusted correctly when if you go to a gainier profile and reduce the gain and the volume stays consistent at all gain levels. (If the cleaner sounds too soft, up the clean sens, if it's louder, lower it, single coils need higher values) Figure out what the clean sens should be for any other guitars you play.
Only then worry about volumes between Rigs.
I would do any leveling in browse mode. I'd pick one Rig, perhaps your favorite, that you forever use as your volume reference, whether you continue to like and use it or not. (Might not be a bad idea to see if this reference Rig's volume is one that is typical of Rigs in general, don't pick an unusually loud or soft one) Whatever Rigs you plan on using in performance mode, edit in browse mode first. Even better, make a copy of that Rig first, perhaps give its name some sort of special character that distinguishes it from raw Rigs. Take that copied Rig in browse mode, (perhaps save it in a special folder for edited Rigs) and do any basic tonal adjustments, (gain, EQ, definition, clarity, Pure cabinet, etc,) and save it. Maybe add some go to effect presets you use in general when you don't need anything special and save that in those Rigs too; then you don't have to reinvent the wheel over and over in performance mode. Then when you create performances, bring in those edited Rigs into performance mode. All your Rigs across various performances should then match in volume. Then you can tweak just about any parameter add various effects to your heart's content and all the volume should match.
Keep in mind that the KPA is the absolute best in volume when compared to any other multi effects modeling/capturing unit out there. It is the ONLY unit that doesn't screw up the volume when you adjust the amps gain, but automatically compensates, as long as the clean sens is set correctly.
One caveat: perceived volume when playing in isolation is different than when played in a mix. You can adjust everything perfectly when playing solo and it matches, but tones that in particular don't have as much high mids will sound lower in volume in a mix. So it's not a bad idea to save the X slot for an equalizer. See if subtle adjustments there fixes any volume inconsistency in a mix. A great way to test that (again ideally working in browse mode and adjusting there) is to play along with a recording on your computer and see how it cuts comparatively to other Rigs. If you're using an audio interface and DAW it's easy. Otherwise, utilize the aux input on the kpa and hook up your phone or computer's headphone output and play along with a recording. Then you can switch Rigs and see if the new one cuts as good as others. And again, do this before using the Rig in performance road.