MCACC should set the levels so reference level at the listening position is attained at 0 dB IIRC. That is awfully loud, at least to me. Sometimes the room (and/or stuff in it) can fool the compensation program (be it MCACC or any other). I have seen programs set the trims low for high-efficiency speakers, but in those cases the system was plenty loud enough.
I would re-run to verify the initial results, and if they are the same then move the mic a foot forward or back, and/or side-to-side, and see if there is a significant change. If not, and the sound is low and trims are low, I would pull up the individual trim levels equally (each channel by the same number of dB) in the AVR.
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley