Arc connects to TV by HDMI-ARC (or eARC)

Amp is wired to passive in-ceiling speakers (I assume that is what you have)

In the Settings for the Arc, add the Sub and add the Amp as surround. The Amp and Sub connect wirelessly to the Arc. The Arc is running the show.

Further note. The Amp doesn't need to be by the TV and it may be more convenient for it to be elsewhere. However, keep it in the same room. The elements in  Sonos HT systems are designed to communicate with each other directly using their 5GHz radios. 

Excellent, thank you, John! It’s very nice to get such a quick response.

My original design is to have ethernet connected from the router to the Amp, for clean, fast data. Would there be a benefit in connecting ethernet between the Amp and the Arc, even though it’s not necessary? The reason I ask is that, as a “wire guy” I feel more secure with the closed system that cabling provides (less EMI, and so on). Nevertheless, I’m fine with wireless transmission.

As you put it, “the Arc is running the show”. I guess the only functions of the Amp would be powering the ceiling speakers, and the portal for user interface only? Sounds like the Arc and Sonos sub have their own internal amplifier. Is that true?

Hi. I understand the desire to wire, but I would suggest keeping the Amp wireless when it is being used for surrounds, as it's the way Sonos HT is designed to work.

It would be fine to connect the Arc to the router by Ethernet, for playing music sources. 

Sonos speakers are active (powered) speakers, and it is fundamental to the system that the Arc and Sub are amplified. I think the Arc contains 11 amplifier-speaker units, but I'm sure you could check that on the Arc's product details on the Sonos site 

Just wanted to add that the amp is not the ‘portal for user interface’.  The Sonos app can connect to any and every Sonos speaker/device/room.  When connecting to Sonos through 3rd party apps and services, such as Amazon Alexa, Google, Spotify, etc, the connection is made to individual Sonos rooms.  The amp doesn’t play any special role in this regard.

Indeed. And when the Amp is used to drive surrounds it doesn't even appear as a room in the Sonos app.  It just plays what the Arc sends to it.

Okay, I’m learning.

He’s also got speakers on his patio, and in his garage (two in each location). He plans to get at least one more Sonos Amp, likely two, to power those. The patio speakers are Sonos (I think by Sonance?), but the ones in the garage are Bose. Since the Amp isn’t used as an interface, and the Bose have no wireless capability, I guess I have to connect an external source to the analog inputs to the amp, yeah?

Likely a Sonos Port would be the ideal device to get the Sonos output to the analog input in those BOSE devices. 
 

I am somewhat persnickety about things, but Sonance is the maker of speakers, Sonos has a marketing agreement with them, so they’re technically not Sonos speakers per se….but since you’re driving them with a Sonos Amp, it probably doesn’t make any difference. 

Are the BOSE speakers passive or active? Active speakers typically require a line level analog input. Active BOSE speakers may require some sort of control input from a BOSE system. Finally, some BOSE passive speakers assume that there is a specific BOSE equalizer in the system and it is not possible to use an external equalizer with AMP.

I am afraid I don't know what you mean by "the Amp isn't used as an interface" but the conclusion that you need to use the analog input on the Amp is incorrect. 

Thanks everyone! I feel much more confident!

I’ve read thru this and other posts...just want to be clear what I’m trying to do and confirm it will work.

I will have a Samsung TV with an ARC port attached to a Sonos Arc (connected by wired LAN), an Amp (connected by wired LAN and then extending to two wired speakers in the ceiling) and finally a Sub (prefer Wifi - wireless connection if possible)

Questions:

1. Can you configure this all to be a Surround Sound config(would that be something like Dolby 5.1?)  I’m not interested in broadcasting to any specific unit, Arc, Amp or Sub in any way - only will broadcast to the joined units in a Surround Sound config

2. I’d read where there may be problems with mixing Sonos LAN connected and Wifi connected devices in a Surround Sound config.  Is that correct?

3. Assuming the configuration I described in #1 above is workable:
   1. Will it play both streaming music from sources like my music library, Amazon Music, Pandora, etc as well as also allow me to play the Surround Sound audio output from the TV when I select it? 
   2. How does this configuration handle the output of streaming music vs the Surround Sound of the TV? Does it convert to stereo automatically when Surround Sound isn’t available?
   3. Does it allow stereo only for the streaming music or another format?   
   4. Do I have the risk of echo that I’ve read about in other posts when playing streaming music in this config?

Yes.  You just add the Amp to be surround speakers in the Settings for the Arc.  But you should not wire the Amp as the system is designed so that the Arc communicates directly with the surround speakers (here, the Amp) using their 5GHz radios.

See answer to 1.  It is fine to wire the Arc

Yes

No conversion is necessary because music is already in stereo.  You would get stereo at front and stereo through the ceiling speakers.  There are separate settings for TV and music sources.

I assume mono and PCM 2.0 OK.  Did you have anything in particular in mind?

You haven’t read anything of the sort for this configuration, and there are no such issues.  You may be thinking of when other speakers are grouped with the HT setup  And that applies only to TV sound.  Music will sync perfectly between rooms.  There is no echo within the HT setup.

Hope that helps.