This volume issue has got to be the number misconception or confusion regarding all AVR, AVP, and Amps.
As mentioned, people confuse this Relative Volume with POWER OUTPUT, which is false.
However, If you still don’t want to have to crank up the volume (which is completely understandable), all you have to do is increase the SPEAKER LEVELS in the manual audio setup in your CX-A5100.
For example, if your speaker levels in the CX-A5100 are set to 0.0, then increase it to +3.0 to +6.0.
Now your Yamaha Master Volume will be around -40.0 with the same loudness as your Sony.
BTW, I absolutely love my CX-A5100 and MX-A5000.
RbhYamahaJvcGuy.