if I’m understanding your post here correctly, I would have thought this was perhaps more a question for Onkyo, rather than Sonos, as their Receiver needs to recognise the audio stream from Sonos has stopped/ended and so then auto-switches back to the TV output, but it’s a difficult issue, as there are times when the music may fall silent between tracks, or a user pauses the music to take a phone call, or maybe select another playlist etc.

I think manual switching to the TV output might be what most users would prefer, perhaps?

Thanks for your reply! I was hoping that the Works with Sonos programming would have addressed the audio input switchback on the Onkyo AVR similar to how you can program the AVR to a specific audio input for HDMI audio pass through when the AVR is turned off (Bypass surround sound system and play audio direct through TV when AVR turned off).

I agreed that this seems to be a function of the AVR itself but would require coordination with Sonos on the development.  

I just completed setting up “Works with Sonos” with an Onkyo TX-NR6050 AVR and Sonos Port - and it all works pretty well - so my thoughts.

Selecting Sonos media that includes the room with the Port turns on the AVR, selects the Port input, and plays (though a sub-second delay while the AVR “wakes up”).  I have the default AVR volume for the Port input set relatively high (90%) - but that enables the actual volume to be regulated by the Port using the Sonos app and the volume sliders are consistent with other zones.  I’ve enabled “Auto Standby” on the AVR which puts it in standby if there is no input for 20 seconds - which works - but, as others note, the AVR input stays with the Port.  This is not an issue for me: If I pick up the Roku remote (really the only remote I use for TV) and tap its “power” button, the Roku / TV / AVR combination all wake up and the AVR selects the Roku (& sets the last Roku-related volume); this happens because the TV is connected to the AVR’s ARC / eARC HDMI output which instructs the AVR to select the right input when the TV is powered on.

A random observation: Initially there was a noticeable audio delay between the AVR & other Sonos zones, so I switched to the Port’s digital output to the AVR.  Delay now gone.

I’m happy - Bravo for the “Works with Sonos” integration.