One question I still was hoping to answer. Does increasing the channel level raise the signal to your speakers at a higher rate than raising the volume?
The way it works is like sighting in a rifle scope. You choose the yardage and dial in for that distance. Shooting shorter or longer will put you slightly off the mark. The average spl is your yardage and the trim level is your sight adjustments in the analogy. Better than a car one I figure.
Lets say you pick 70db as your matched level. You play the channel test tone and adjust the trim per channel so it reads 70db on an spl meter per each channel and sub. So, when the average level is 70db, you are where you should be where all channels sound balanced. I usually start with left and right, blend in the sub with crossover, and then the other channels. And revisit with content. It can take a bit, but once its dialed in the pans become smooth and it wont sound like speakers anymore. Just a cohesive soundfield.
When you drive all channels from the onboard amps, the per channel spl will track nicely with eachother over a wide volume range. When you add an outboard amp you have to check after your initial trim set at 70db that the channels track closely at say 50db and 90db. They wont usually. You will have to adjust the gain so it better matches the onboard amp gain/spl output. Then reset the trim and testest at 50db and 90db. You will never get it perfect, but you can get so close it isnt really audible without test tones/pink noise. Same is true if you mix speakers with wildly different impedances or efficiency ratings.
Hence, sighting in a scope.
