You must have easy to drive speakers.
The sensibility on the Kefs is rated at 86dB
The incoming of source volume / material is what is varying the loudness… Source volume is different. Let’s say with blu-ray you would volume at 40 @ 100db. From netflix volume at 40 @ 92db, amazon prime volume 40 @ 89db, bbc news volume 40 @ 102 and so on.
Not the amp or avr what is doing it.
Also.
Amp showing volume’s like 50 or 20 or 120 has nothing to do how loud the sound is to rest of us.
I just find it really funny each time it comes up.
Git that , not the only one to experience a reduction of db with the specific amplifier. The value on the little display on the unit goes from 1-60 not actual measured db. Means something to the ones that have a unit. But youre right loudness is subjective.
So differences in loudness of the source material compression of data and the reduced performance due to heat will vary the measured volume of these little budget amplifiers im thinking. Pretty sure the electrical line power from the street is stable measured around 124 volts if i remember.
Although it could be line power notice the same reduce loudness on the AVR at times not sure if its voltage or heat combination of both.