Lucid - that is really useful thanks.
The plus is I have the Atmos speakers on a 14 day trial so I can see how they sound in the room. Sounds like they will be going back and i'm better investing that money in a really good sub and stick to a 3.1
It is owned, would you recommend cables over the wireless solution? Does it make a big difference?
When using Wi-Fi for wireless rears (as opposed to Bluetooth) - which is what the Musiccast speakers do, they're Wi-Fi - and combining that with movie surround which might already be compressed if you're watching streaming content; it never gets any better than DD+ for Atmos (DD uses lossy compression, so DD+ does the same for streamed Atmos-enabled content), then wired or wireless for the surrounds isn't that big a deal. Other stuff is going to overshadow the wired/wireless debate such as the speaker quality and room set-up.
The thing with wired is it gives you peace of mind. Wired always works unless the cable is broken.
It also gives you the opportunity to use speakers better suited to the job. You've got to pack a lot of stuff into a wireless speaker before you get to the parts that make sound. As much as I like Yamaha gear I still have to be pragmatic. One Musiccast 20 or 21 wireless speaker is £180. A pair then is £360. That same £360 buys a hell of a lot of performance in a conventional speaker that could be used for surround. Another view is you could spend less on conventional speakers and still equal the Yamaha performance. If money isn't the main consideration then maybe it's aesthetics - a speaker being the right colour or size - or simply practical? "I don't have a mains socket nearby"
Wireless is improving, but not all wireless is the same. Thinking about your sub, there are various flavours of Bluetooth including AptxHD and low latency, but they all use some form of compression and/or introduce some delay or signal loss, or both. Cables don't do that. I can see the appeal of wireless compared to losing a couple of hours on your hands and knees hiding a bit of wire, but I've never lost my surround speakers or sub because the router needed to reboot or some neighbour decided to mess about with their wireless settings and it knocked mine off.