Can I Or Should I Connect My AVR to Sonos 5.1? It's Complicated....

No you can't, and no you shouldn't. What you describe is not possible, and I would recommend against Sonos for home theater, if you like 5.1. If you don't want to take my word for it, search these forums for the myriad discussions about the lack of DTS and DD+ support, the limitations of nearly every tv around pass through surround, etc. Sonos home theater was a terrible mistake and I urge you not to repeat it.

Thanks for the reply Tyler and noted. I like 5.1 but it's not something I necessarily need to have in multiple formats. I had a demo on Sonos 5.1 with a playbase at Richer Sounds since posting and for someone of my lack of sophistication, I felt that the sound was good enough and not a massive obstacle for me, considering the difficulty of replicating my current set up with all the wires and flooring upheavals at my new house, coupled with the frequency of how often I watch Blurays. I'm happy to sell on my AV amp and speakers on the basis of the demo to have an easy life. However, I still have the unanswered questions as to whether the 5.1 sonos system could be brought into the whole house set up for music and still sound good (or good enough) in the room with the 5.1 set up? And would an LG OLED (specifically) have a good enough pass through for sound?

Here's the problem: The playbar/playbase has only a single SPDIF input. SPDIF does not have sufficient bandwidth to handle uncompressed 5.1. So it needs compression, The playbar can't handle streams compressed with DTS or DD+ (these are most sources). It can only take Dolby Digital 5.1 (not plus). While some older LG TVs have been confirmed to pass through DD 5.1 on SPDIF if DD 5.1 is the source, the TV won't transcode anything. Even if your TV will passthrough DTS, the sonos won't play it. So DTS, TrueHD, DD5.1+ and other formats will need to be output from the TV as PCM 2.0 (no discrete surround channels). The Sonos will then attempt to upconvert that signal, but it won't be surround at all, it will be stereo coming out of more than 2 speakers since the discrete channels were lost. If you hope to get surround even from a DD5.1 source, you need to confirm that your TV will passthrough DD5.1.

Receivers don't typically transcode either, so same problem. If you try to retain some speakers or sub from your old setup, you'll have sync issues, if it works at all - I've never seen a receiver that lets you simultaneously output on SPDIF and speakers while allowing you to choose which channel goes where, that doesn't mean yours doesn't, but the burden of research is on you.

EIther get a Sonos Connect and keep your AVR and speaker wires, or ditch it find something that will transcode and go all-in with Sonos (playbar, pair of play:1 or play:3 surrounds, and sub). Sony and Oppo make bluray players that transcode, a Sony PS4 will as well. Without something to transcode, you won't even get surround sound out of Netflix with your $2000 sonos 5.1 setup.

I agree with most of what @tyler1101 has said. Specifically, forget all thoughts of some combination of your existing AVR with Playbar/Playbase etc.

However, I have a LG OLED TV and a Sonos 5.1 system and it works great for me. I am happy with the sound quality of DD5.1, I do get 5.1 with Netflix and I have a Samsung Blu-Ray player that transcodes DTS to DD5.1 (not totally sure Sony BRs do), so that gets round that problem.

It integrates perfectly with the rest of my Sonos system, but then that is fundamental to the nature of Sonos.

So I think you would be happy with the result, BUT unless you are really sick of the wires, I still agree with @tyler1101's conclusion. I didn't have an existing 5.1 setup, but you do. And it doesn't need the workarounds that Sonos needs. And the sound may be better - it depends on the system, clearly, but it is almost certainly capable of playing higher quality audio formats.

You can, as @tyler1101 suggests, use a Connect to play Sonos through the AVR. It is possible that you will get sync issues between that and the other Sonos players because of audio processing in the AVR, but there is often a setting that can eliminate this.

You could take advantage of Sonos' generous returns policy to try a Connect.

Will add my 2 cents here.

First the simplest question around if you would need anything else to include the 5.1 system in your music playback - no, you won't.

Second, regarding the DTS/DD+/5.1 issues mentioned by others - you'll want to double check, but LG OLEDs should pass through DD 5.1 just fine and should also transcode DD+ to DD (meaning you'll get 5.1 with streaming services like Netflix). Only remaining issue would be DTS from your Bluray player, although yours might (and you could certainly find one that does) transcode DTS to DD.

Third, regarding whether you should keep your AVR - I'd lean heavily towards no. Assuming your AVR actually has an optical output (most I've seen do not), you'd be able to insert it as basically an expensive HDMI switch, but there's going to be no benefit (and probably some complications) from doing so. With digital sound, you're not going to get any quality boost from passing it through an AVR. The AVR may also not have the DD+ to DD transcoding capabilities that the TV does, meaning running sources through the TV would actually yield better results. I suppose it's possible that it'd allow you to simultaneously output to the PlayBar and your current sub (saving you from having to buy the Sonos one), but you'd need to test that yourself and I can imagine there being syncing and crossover issues that would diminish the sound quality.

In case of doubt, i was suggesting keeping the AVR instead of getting Sonos 5.1, not playing one through the other. No combination of elements is even worth trying, IMO.

Are you 100% sure Lg TV's down transcode DD5.1+, into DD5.1?
I believe my LG OLED 55B6 just passes through what it receives to optical, including DTS:X displayed on my AVR.
People are reporting DD5.1+ from newer Netflix stuff, which is no good at all for sonos stuff.

I am 100% certain that my LG 55EF9500 transcodes DD+ to DD. It does not transcode DTS.