(Well, this opinion is never going to get marked “best answer”...;-)  If you are building it, you can change it beforehand.  I would do so.  Without a furniture plan, it’s not clear if you are doing a residential living room, or a multi-seat theater room, or even a commercial (so-called) “multipurpose room”.  So you have a high-ceilinged, 30-foot x 30-foot x 45-foot right triangle.  Make it smaller and repurpose the point of the triangle be your equipment room or media storage, with a door to the outside hallway.  Most people would rotate the whole thing 90 degrees and put the TV on the 30-foot wall, and turn the alcove into a bar.

If not, this room is too big for any set of small speakers, which the Arc is.  Worse, attempting to let the Arc (or any of the “fake-Atmos” soundbars like the B&O Stage or the Sennheiser Ambeo) reflect off the side walls and the ceiling, is doomed to fail.  You don’t say if your vaulted ceiling is sloped, which I suspect it is.  So any built-in standardized reflection calculations, even with the measurements & adjustments (that they don’t tell us what they are doing!) is just going to miss your viewers’ heads.  You have labelled the hypotenuse “bifold door” which I hope is a misnomer: either get a commercial meeting room acoustic pull-out divider, or if it’s fancy residential get glass sliders and synchronize some draperies inside them.

If you must keep this shape, you are a prime candidate for ceiling-mounted height speakers, 2 subs or maybe even 3, freestanding large left/center/right speakers and aimable or drop-down motorized (because of the location on the hypotenuse) surrounds.  Oh, and sidewall absorption.  Plus a “real” cinema design professional, who will be well worth his/her cost!  Go ahead, everybody else here, prove me wrong on that point...

Thank you very much for your comments.

The room is an entertainment/BBQ room that will be used for social events (at a private house). We will have a built in wood BBQ and a full kitchen against the wall where B and C is. The bifold doors are glass panel doors that ‘collapse’ when you open them to maximise the opening (so 3 panels move to the left and 3 panels to the right where they stack against each other on a track) - this will obviously only happen during summer (of which we have little in the UK).

The ceiling have 5 different angles and are sloped.

Neels

5 different angles on the ceiling?  Forget my height speakers recommendation, and definitely don’t try to use any Atmos-simulating speakers.  Stick with basic 7.x, or even 5.x.  Maybe even pull the speakers sooo far in from the walls to simulate near-field sound if the audience is small enough to be localized.  If not, just chuck it all and put in 3.1 with full-sized L/C/R speakers and don’t worry too much about the quality of the sound since people are going to be milling about most of the time anyway, or maybe always watching football.  (Then grab another room for the owner’s quality movie-viewing!)  Or ask a sound design professional for maybe some locality-of-sound trick -- so you can *hang* *all* the speakers from the ceiling, creating an enveloping but not really movie-accurate soundfield, like the way those Bose soundpods hang in restaurants (not exactly mono all around, but definitely re-processed stereo).  Random ideas, worth every penny spent… Good luck!

odEdit: P.S.  Aahhh, sorry, you were looking for a Sonos solution: 1 x Sonos Amp, plus two front left & right speakers (from third party, high-efficiency (=loud per watt)), plus 1 x Sonos Sub (which isn’t enough but better than not), plus 2 x Sonos Five mounted high mid-room, and angled down as surrounds.  Not brilliant theatre; merely functional.]]

Thank you very much

That sounds like one ugly room, I’d suggest something like the stuff below, maybe some in-wall or in-ceiling speakers would work better though.

Some speakers like Klipsch that are very high efficiency would be on my list.

https://www.crutchfield.com/p_700P86F5C5/Klipsch-RP-8060FA-5-1-2-Dolby-Atmos-Home-Theater-Speaker-System.html

Maybe with a high-end AVR with a very good parametric equalizer and audio calibration system so you can get to a baseline setup and tweak that for better sound.

Not recommending this one, just giving it as an example of what to look for. I’ve had Denon and Yamaha systems that were very good.

https://www.crutchfield.com/p_440AP1582B/Rotel-RAP-1580MKII-Black.html?tp=179

Feed it from a Sonos Port to get your music into the system.

https://www.sonos.com/en-us/shop/port