I don’t understand why you’d want to connect an AVR to an amplifier. What are you trying to do?
Some people don’t know the difference between an AVR and an AVP, some just use the terms invariably, like I use to 😀
He would connect an external amplifier to the preouts of an AVR (if/when it has them) to improve the sound quality of an AVR. Active internal power amp sections inside an AVR degrade the sound because the DAC, etc are in the same chassis, tied to the same power supply, etc.
An intermediate grade solution is....for example, Sound United has some AVR offerings that can disable all internal poweramp sections and run an AVR in pure multichannel preamp mode.
The high fidelity way of doing it is to get a dedicated high fidelity multichannel preamp processor designed/built from the ground up and pairing it with the same external power amps audiophiles like to rave about.
For those who don’t know such details, multichannel is for movies. For those who do, multichannel is for music.