I tried very similar but not that, I think the difference was auth settings.

It has seemingly gotten me one step closer because it's actually popping up and asking for credentials when I click Check Names, but it's still not working.

Time to fiddle some more.

Can't remember off the top of my head, but I think there's an additional setting within exchange that needs to be set for remote connections... Do you know what version's running there?

There is a way, but I can't remember how to do it.  I used to have my Exchange & Outlook setup that way.  Now I have to use the shit known as Lotus Notes.  >-|

This has now worked.

I had to get inside the network so my new version of Outlook (that supports multiple profiles) could sort its shit out then I could add the OWA profile.

I left the network and it seemed to sync as it should. I'll find out for sure once I get home.

Yep, tethered on the train and it's synced up. Bye bye god awful OWA.