Which model YAMAHA?
AUDIO 1 and AUDIO 2 are inputs to the receiver.
On the older receivers digital audio inputs, such as HDMI, are not usually converted to analog audio for the audio output jacks. Try playing Tuner while you explore audio output from the YAMAHA.
Audio 1 and Audio 2 are inputs on that receiver, nothing will get to the Line In on the Sonos. The only line level outputs I see are the AV out, or Audio out.. Which probably requires a bunch of programming on the amplifier, I’d guess.
But certainly the Audio Out, assuming all the programming on that receiver is correct, should be working.
Many amplifiers don’t convert digital inputs (the HDMI connections up top) to analog outputs, but it’s worth double checking the manual. There was no statement made about what content you’re trying to get in to the Sonos system.
Were it me, I’d adjust the line settings on the Sonos to ‘fixed’, not ‘variable’, at least until you get it working, then you can make alterations as you feel fit, but that affects the line out, not, if memory serves, the line in.
Edit: @buzz types faster ;)
@buzz and @Airgetlam, you both responded so quickly that I hadn’t pushed send on my edit to the original post which addressed a few of your questions and comments.
First, the receiver is a Yamaha RX-V373. Goal is that once I can hear the tuner (current setting on the receiver) on the Sonos speakers, I’ll hook up my turntable (unamplified) and CD player to the receiver.
Secondly, I’d figured out that the Audio 1 and Audio 2 were inputs, so narrowed it down to the Audio Out jack. Can’t figure anyway to program the amplifier, but I can take a look at the manual tomorrow.
Finally, I’ve taken @Airgetlam’s suggestion and set the inline setting on the Sonos app to “fixed”.
Still no luck, however. Wondering if I need to remove the Play:1 and Roam SL from the “system” and add them back in?
Thanks for your assistance to this point!
One very unfortunate detail would be if the receiver’s Audio Out jacks respond to the receiver’s Volume control. I don’t expect this because the manual suggests that these jacks can be used for audio recording.
As far as the receiver is concerned CONNECT is a tape recorder.
@buzz
Thanks. I guess I’ll try Sonos Tech support tomorrow if no further suggestions, but given past experience, I’m not very hopeful. Very frustrating.
I currently have Receiver set to Tuner —>Audio Out—>Connect Analog Audio In ….but no sound out of Sonos Play:1 or Roam SL.
Removing the Sonos speakers and adding them back in shouldn’t make a difference, it wouldn’t hurt, but it wouldn’t help, either.
The challenge, at least for my perspective, is that this receiver isn’t really designed for adding an external device such as a tape machine (or the equivalent Sonos CONNECT/Port). But that being said, there should be audio coming out of the Audio Out jacks. And it should be a line level signal, which is what the Sonos line in, no matter what Sonos device, is looking for.
My supposition, without looking up and reading the manual, is that there is some programming involved on that device, in order to get the audio to actually come out those ports. But the Tuner is a great place tipo start, it reduces some variables, always a good thing, especially if the tuner is playing on speakers currently connected to the speaker ‘posts’ (on the right).
No sweat about the editing, either 
I’m frequently rereading my posts, checking for poor typing, and clarity, something I tend to miss the first time I post, no matter how often I think I check ;)
You may want to contact Yamaha’s CS, and check with them about how that output gets activated, and what restrictions there might be. It would be annoying, for all of us, if they turned off that output when playing the tuner, for instance, in order to protect copying music…
If you don’t mind sacrificing an RCA cable you can cut one end off and wrap the wires around the plug for a set of headphones. That will detect outgoing audio, usually at a very low sound level but it will tell you if an output is providing a signal.
The two center conductors should go to the tip and ring, the outside conductor/shield to the shaft past the ring.
You are using RCA to RCA cables?
Do you need to select the “source” that goes to the output?
Have you tried the AV Out connection 6? Again, you may need to select the source.
In the SONOS Room that you want to play the receiver select Line-In.
