I assume you mean Sonos Arc Ultra and not Samsung for the soundbar?  Because the Amp and Sub will only connect to a Sonos soundbar. 

Given that, no Ethernet needed, as long as the Arc Ultra, Amp and Sub are in the same room.  They are made to connect wirelessly, and problems can arise in ping times if you connect via Ethernet.   Other than that, you need an HDMI from the Arc Ultra to the eARC port on the One Connect box, power to the location of each unit (Arc Ultra, Amp, Sub), and the ceiling speakers need to be wired back to the Amp location using in-wall certified speaker cable.  Your electrician should put a box in the wall with speaker wire connectors and a wall plate for the Amp like this:

How do you intend to use the ceiling speakers?  Sonos only supports using the amp for rear audio channels, ideally not placed in the ceiling.  You can get away with ceiling speakers if your space restricts anything else, or you value the aesthetic value over sound quality, but it’s not ideal.

The Arc is designed to bounce audio off the ceiling (and walls), so additional audio coming from the ceiling (tat should be coming from the rear) isn’t good.  You would get a better experience with amp + speakers in the back wall, or even better, using Era 100s or Era 300s (you can connect by ethernet if you want, but no needed).

I get that you want to avoid wireless, but I don’t think wired really gives you the best option these days, unless you go all out with separate front speakers, side speakers, and maybe ceiling speakers.  The latter isn’t an option with Sonos.

Just my two cents….

Not knowing the layout of your home and the room you want to use for Home Theater you might do better if you consult a professional installer. They may recommend Sonos or suggest a traditional setup or both depending on the rooms.

Thank you.

Yes, jgatie, I meant Sonos Ultra Arc not Samsung Arc.

Yes, melvimbe, I intend to use the In ceiling speakers as rear audio channels placed behind the sofa. The TV is on the end wall and I’ve placed the ceiling speakers (square with a green cross) on the image below. They could go even further back above the dinner table -Its a large room with open plan kitchen further behind.

Question:

• if I pair up the in ceiling speakers as rear audio with the BEAM for the home cinema, can I also use them separately to provide background music to the room when the TV is not in use?
• Any thoughts on where to place the subwoofer? Its a ceramic floor and my plan had been to put it in a cupboard on the left hand side of the sofa. I’ve been told it has to be touching the floor but it doesn’t matter if it is enclosed?

Since you are going with in-ceiling speakers for surround I would not recommend moving them further backwards of the seating area.

The sub should not be placed in a cabinet. In fact, you may need to experiment by using a long extension cord to move the sub around the space to determine where the low-end is optimized. I would not move the sub backwards beyond the in-ceiling speakers into the dining area.

The speakers used as surrounds can be used without the TV for streaming music. However, as they are surrounds and bonded to the Sonos soundbar it too will play along with the surrounds.

If you want in-ceiling speakers to work independently of the home theater, you’ll have to purchase another pair with another Amp.

Also know that the sub is part of the home theater and if you want more low-end for an additional set of in-ceiling speakers you need to purchase another sub. 

• Full disclosure if you want you can break the bond of the sub from the home theater and bond it to a second set of speakers, but you’ll have to repeat the process to get it back to the home theater. That process is more work than you imagine not to mention time consuming.

When surrounds are added to a Room they can't be used independently. You could use all the HT Room speakers for music by selecting Full Mode for the surrounds.

Sub touching the floor, not heard that before, one of mine isn't. Enclosed is usually a bad option, maybe lay it flat under the couch if there is nowhere else to put it.

Thanks all for the inputs. I now understand the in-ceiling surrounds can’t be used independently without considerable hassle. Given that, and given I’m not so so fussed about perfect sound for the home cinema, I will likely proceed with the default setup of NOT having the in-ceiling speakers for surround. For me, I suspect the Ultra Arc and Sub will still give a pretty good result for TV watching. I then focus the in ceiling speakers on the use case of just having background music on whilst we are cooking or having dinner. 

As such I’ve changed my design as follows. I’ve turned the in-ceiling speakers into 4 to get better coverage across the room. I’m guessing a bit here but I suspect just having 2 speakers in such a large open plan kitchen, dining, living room would not be sufficient. 

My wiring diagram is also updated based on the advice. Thanks!