I'm glad you are starting to make sense of things.
If you've got it working, I would recommend doing everything through the app. You will have much better control with that than the AVR.
I agree, you want your Subs to read between -7 and -10 if possible. Positive numbers mean digital boost is being employed, and that leads to distortion.
In my book, as long as each of your front subs are set within say 1.5dB (arbitrary, but closer would be better.
) of each other, then the summation of the two should be good.
Look forward to your report once you get another chance to play.