As I type this my PC is reading the Data from 3 of my discs successfully.
My dual slot USB dock took longer to arrive than I would have liked, but it arrived today.
I slotted two discs into it, added a third in my SAYA bay on top of my PC and started up 'NAS Data Recovery'.
The there drives were easy to identify in the program, you have to tell it there is one drive missing, then it searches the discs and identifies the raid structure, which it did.
From there it 'mounts' the array and you can see the folders in an 'Explorer type' window, Without a License it just proved the file structure was there, you are not able to save anything.
So I bit the bullet and invested $99 in the license and then I could save everything so far. I have a 3 TByte drive as a data disc in my PC and have cleared space on there, I had less than 2 TBytes on the NAS.
The data is reading at about 25 to 30 Mbtyes per second, which is not rapid but not ridiculously slow.
Next questions are why and where next? The NAS was switched off for a couple of weeks and started up OK when I came home, then died without warning on a hot afternoon two weeks later. I can't believe the temperature was the issue as the log never even said it had set the fan to high.
I can't see I will ever trust the 345 again, but I don't know what to replace it with.