You usually have to 'tell' the TV which audio output to use, internal Speakers, Optical Out, ARC Out or Line Out (depending on your kit).
If your TV and AVR are both ARC capable you you send audio via the HDMI cable which connects the AVR to the TV - you first need to set CEC to On on both devices then configure the TV to ARC Audio Out.
Your TV HDMI Input may be a limiting factor in terms of the audio you can expect to send from the TV to the AVR as many TV's only support stereo audio on their HDMI Inputs. You may want to consider 'streaming' the movies using one of the other devices you have connected to the AVR!
List the make and model number of the TV, AVR and connected Source devices you have in your system.
Joe