How do I stream Tidal over wifi

[Will]

'tis OK I worked it out thanks to google!

Real pity it doesn't work from a phone or a tablet though

You can add a Google Chromecast Audio to your system and use a phone or tablet to control streaming of Tidal to your Expert.  All connections are wireless apart from an optical cable from Chromecast to Expert.  This works well and sound quality is surprisingly good considering the low cost.  Set-up is straightforward.

https://store.google.com/gb/product/chromecast_audio

Dumb question maybe… how does the Chromecast Audio connect to my devialet?
Is it via optical or via wifi ?

You will need to purchase an optical (toslink) cable which you can then use to connect your Chromecast device to the optical input on your Devialet.  You will need to set up Chromecast on your home wifi system (the instructions on how to do this come with the Chromecast).