Basic rule of thumb is that doubling the wattage results in 3db increase. Similarly, doubling the distance is 6 db decrease in level. "Doubling" of perceived loudness is around 10 db.

Decent article at https://www.musiciansfriend.com/theh...ifier-loudness.

And a pretty good thread (including charts) on distance vs SPL at https://forum.blu-ray.com/showthread.php?t=151904

The CBM's are pretty efficient at 91 db @ 1 watt db / 1 m. How far away is your main listening position? You may be fine with the 95W RX-780. Looking at the pic of this on Crutchfield, looks like it has preouts for Fronts, so you could always add an external amp if needed.