At -5 the average should be closer to 80dB, peaks up to 20dB more. Might want to tell us more about how you ran Audyssey (the steps you took for mic placement, number of mic positions). Maybe all settings for speaker level and delay (distance), too as well as crossovers. One thing that comes to mind is that the avr may set Audyssey Dynamic Volume to on, if so try it off.
PS you probably have an input level adjustment, not likely you ran into it by accident, but might want to check that.