I have a Sony Bravia 65 Tv and an external audio system with a roku streaming device. Since hooking up roku, tv switches from audio system back to tv speakers by itself. I have to change sources in order to change back to audio system.
What is happening is the CEC function is causing the AVR or the TV to change inputs. Usually CEC works just fine, but occasionally it can be a bugger. In the Roku, go into the settings menu and find One-touch Play and turn it off. You might have to disable CEC in your AVR or TV as well, but try it just in the Roku first.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.