About the gain difference issue, sorry if this sounds obvious but it's usually a matter of volume going back in. Make sure the tracks you reamp from Logic (and your DAW master volume) goes back into your interface at +/-0 Db. If you lowered the volume of the track or the master volume in your DAW, the gain will be lower
I think it's got more to do with what luntho said above that the Audient sends everything to its outputs. Even if you have specifically designated just one track to be outputted to the KPA. But this is only one line of exploration.
Hopefully will come back with better news.