Here is a diagram that shows a typical Arcana/Projector setup:

You would add your Shield/Xbox to the HDMI switch and then cable the switch to the Arcana input and then the HDMI output (without ARC) goes to the projector and the HDMI output (with eARC) goes to the Sonos Arc.

Another image that may help clarify things too:

That's brilliant Ken cheers... but my next question is....what hdmi switch would be good for this setup, any recommendations 

I haven’t fully researched to see what might be a decent switch to use in the above setup personally speaking, but @melvimbe on the forum here has suggested the SkycropHD 4K@60Hz 5 Port HDMI Switch with Remote, the 5 ports though are perhaps a little more than you need.

Anyhow, after a quick look for something with fewer ports, I would maybe suggest this one below, or one with a similar spec:

https://www.amazon.com/ROOFULL-Switch-Vision-Switcher-Compatible/dp/B07D3QD59P/ref=sr_1_3

Thanks again

Just to clarify, I don’t really have a recommendation for any HDMI switches, splitters, or matrixes.  There are a lot of options out there with lots of different features at different price points.  Best to know what features you need and pick one that is well reviewed.  Both options are fine, but of course may need to be replaced as your needs changed. 

I personally use HDFury’s Vertex2 which is overkill for most people’s needs.  HDFury will even tell you to use a cheaper switch in most cases.  I went with that option as I have a setup with multiple TVs with different capabilities and I wanted auto switching.