Design of new kitchen-diner

@AjTrek1 thank you for the very detailed response.  That sounds like the best way forward. I am unsure whether there would be sufficient room in a fascia above the bifolds but if not it will certainly be possible to fit ceiling speakers just above the bifolds. 
it will be a few months before we are at that stage, but something to look forward to in the new year. 

Hi @NickWr 

Glad you think my suggestion may be doable (i.e. in the facia above the bi-folds or in-ceiling in the relatively same position). Here’s another suggestion to consider…

The Sonos Amp can power six (6) Sonos In-wall or In-ceiling speakers by Sonance (only).  That said you could stratigically position two (2) more speakers in the space. Said installation could be done at time of construction or pre-wired for installation at a later date for budgetary considerations.  

Pre-wiring for In-wall speakers for the TV could be done as well.  You could use a Beam or Arc mounted on a cabinet (below the TV) in the beginning to prevent marring the wall; if you’d like to consider in-wall speakers at later date.

Also, if using the Sonos Amps inside a cabinet (that is part of the construction) remember to run Ethernet and electrical inside (as I mentioned in my previous response). I would also run Ethernet and electrical behind the TV for a clean look. Ethernet for the TV will be handy for updates and smart TV apps like AppleTV, Netflix etc.

Just a few thoughts 

Note: Speaking of two additional speakers it appears they could be installed in the facia that runs the length of the wall across from the bi-folds and over the door way. IMO one would be placed centered in the area that overlooks the sofa in your 3D rendering and the other behind the sink area.

Thanks @AjTrek1 - all good points. 
I am still undecided how to configure the ceiling speakers in terms of channels; I.e. would it be better to have four speakers above the bifolds in two sets of stereo pairs (so running along the window they would go LRLR) or one big stereo zone (LLRR)? I suspect the latter. 
if we also went for another pair on the other side of the room as you suggest, it’d probably have to go:

L L  R R

  L     R

The cost of that setup is starting to get fairly uncomfortable if using the Sonance speakers, but I see that is the only option if you want trueplay and/or 3 pairs powered by 1 amp. 

Hi

Actually, when using multiple pairs of speakers in a space as yours traditional logic is to set the Sonos Amp in mono. In that setting no matter the position of the listener the sound is the same with no loss of content. For example the listener doesn’t hear an instrument  that sounds miles away.

Stereo is best enjoyed with only two speakers forward of the listener. In your space the goal is more about coverage than stereo separation.

You might consider volume controls for each pair of speakers to better control the level in certain areas or turn a particular area off by lowering the volume. 

As I mentioned previously you can pre-wire to add the two (2) additional speakers later for budgeting considerations. You could mark the locations with a wall picture.

Note: The additional 2 speakers could also be wired to another room as long as playing the same source in that area is not prohibited.

Note: Yours is an aggressive project if you decide to take the route I’ve outlined or a variation. I would highly recommend consulting a professional installer. Not just to get it right but also for warranty of the installation. Dollars spent today with a professional may well be worth it later on.

@NickWr

Hi

I hope you get an opportunity to read this and my previous post above. I have one more option that you might consider that negates running speaker wire for in-wall or in-ceiling installation as well as measuring for openings in the wall and may provide better control.

I’ll use US measurements in this explanation. Installation of the proposed speakers would be mapped prior to installation of the finish wall surface.

During construction of the under-wall consider running a 1x6 board at the top of each wall and a 1x4 board at the bottom and 1x4’s spaced every 18 inches in between. Doing so provides a nail surface for the finish wall.

Now let’s consider wall mounting Sonos One SL’s in the position where the in-wall speakers would have been. The installation of the 1x6 allows placement of the One SL’s (with appropriate electrical along side it) without having to worry about locating a wall stud for installation of the speaker wall mount. A short power cable would be used as shown here. I’m sure the same can be found in the UK.

Note: One of the speakers should be a Sonos One with voice assistance capability.

Each speaker would be named accordingly such as Kit 1, Kit 2, Kit 3 and so on. Those speakers could be set as stereo pairs according to your design. The stereo pairs could be broken at any time depending upon your need. Volume would be controlled by your device either individually or as a group. 

I hope this helps as well.

Thanks @AjTrek1, food for thought. I have a month or so to ponder it before the build gets to the appropriate stage. 
Your advice is much appreciated, thanks for taking the time.