Yamaha home cinema to with Gold Phantoms

[Snoopy8]

I'll get the electrician to pull the cables to 3 Phantoms and then I'll Stereo them to my other speakers, so like that I would just need to pull cables to 3 of them I presume. 

No, you need to use Ethernet cabling for all the Phantoms and Dante adapters, cabling for all of them. 

Sounds good ! so for this set up, what would you recommend for the 7.1 ?
AVR: the JBL-SDB-55
Front L C R : 3 Phantoms premier Gold 4500W
Rear : 2 Reactors 900W

Mixing the Gold and Reactors is a problem, because they have different latencies.  Not sure whether the problem has been resolved in latest Devialet firmware? The guru @njaiswal had lots of issues mixing Golds and Reactors, which required even more equipment to resolve.  More importantly, he should be actively involved in this thread.

adapters : PoE Network switch and Ethernet to Optical adapters, any advice on what equipment to use here ? or any random one with good quality would work ?

Any PoE switch is OK (I like Ubiquity, but more expensive) and you need one with enough PoE ports to cover every Dante adapter.  Get a better optical cable with a better end plug to ensure you never have contact problems; the guru suggested the cheapest Audioquest Pearl and it need only be a short one.  Just to be clear, the connection is:
ethernet cable -> adapter -> optical cable -> Phantom

Office : 2 Phantoms premier gold 4500W
AVR : Need a small AVR with phono and optical that can be linked to 1 sub and the 2 Phantoms and eventually 2 8k HDMI inputs as I don't have anything else to plug there

Must you use a AVR?  AVRs are not good for stereo music.  Suggest getting a stereo preamp.

So ideally, I would be able to command the 6 gold phantoms with my phone at anytime, then also connect it to the AVR receiver and have the 5.1 system

Not sure the JBL has a phone app?  Let me answer your earlier question on 7.1 vs 5.1 here.  I was an early 7.1 adopter, but moved back to 5.1 when I had to shift.  I do not miss 7.1, so my suggestion is go 5.1

 Any opinion on the Sub ? 

Do you need a sub when all the Golds themselves produce lots of bass?

Here I made a simple diagram of the living area. 

OK, you are getting SERIOUS!  Before you go further, you need to know the details and implications.

Firstly, Dante adapters.  The Auvitran adpater is now sold by Devialet themselves and you need to email professional@devialet.com (Professional Enquiries).  Another option is Digimedia
https://www.micromedia.ch/?product=digim...ca-tos-poe

Each of the Phantoms need to be enabled in direct optical mode to reduce the latency of the Phantoms.  Once you do that, they become effectively an active speaker and controlled by the JBL.  You will no longer be using the Devialet App in a Dante network.  Hence, in your diagram, the Phantoms with the stereo connection need to be ethernet cabled as well and will need the Dante adapter.

The Dante Controller (free software than runs on any PC) in my original diagram is used to configure where the inputs and outputs are. To use stereo in larger room, you will configure that pair within the Dante Controller.

Important that you get JBL manual and read that in detail to see how multi room works, how it is controlled, is there a phone app etc. (Sorry, I have not used the JBL).  You have to find out whether the JBL can deliver what you need.