If you run the room correction program in the AVR it should compensate for the gain difference. Otherwise, adding an amp may or may not change the volume depending upon the gain of the amp compared to the gain of the internal amp.
Most people can reliably detect well under 1 dB when switching between components. But bumping the volume on a given component takes about 1 dB to be noticeable.
I have six or seven AVRs around the house (yes, pales to the component count of John and others). One, a Sony ES, really struggled driving a 5.1 system, and its multichannel rating was way below the 2 ch rating. All the others did fine with nominal 8-ohm'ish speakers and didn't noticeably degrade with multiple channels driven. Sighted testing, no measurements. I only noticed because the Sony was really poor compared to the rest.
Others have already discussed the potential benefits of adding an amp. IME expectation bias is very strong and I suspect most folk buying an external amp for their AVR do not need it. But this is the audio world wherein the exception makes the rules so everyone must have an external amp to play... And it is the easiest "upgrade" for many people whether it helps or not. I would guess most of those folk would be better off adding room treatments or upgrading their speakers.
Most people can reliably detect well under 1 dB when switching between components. But bumping the volume on a given component takes about 1 dB to be noticeable.
I have six or seven AVRs around the house (yes, pales to the component count of John and others). One, a Sony ES, really struggled driving a 5.1 system, and its multichannel rating was way below the 2 ch rating. All the others did fine with nominal 8-ohm'ish speakers and didn't noticeably degrade with multiple channels driven. Sighted testing, no measurements. I only noticed because the Sony was really poor compared to the rest.
Others have already discussed the potential benefits of adding an amp. IME expectation bias is very strong and I suspect most folk buying an external amp for their AVR do not need it. But this is the audio world wherein the exception makes the rules so everyone must have an external amp to play... And it is the easiest "upgrade" for many people whether it helps or not. I would guess most of those folk would be better off adding room treatments or upgrading their speakers.