Thanks for your long reply Raum.. I feel really sorry for your troubles; my what a song and dance. In the end, after 2 hours of wasted time, i gave up last night and did a free 3 month trial to iMusic; then the music on my macbook uploaded within minutes to the icloud drive and populated on itunes on my imac.. quite ridiculous. before the trial is up either there will be a way, i will have downloaded all of the songs onto the imac or i will be back to square one as i am not paying again for something that should already work.
Another thought; I have noticed that OS Sierra, like virtually all updates before it, does not enable all software and all external devices, connected to a computer running it, a trouble free experience; I recently moved from iphone to ASUS and I am very impressed and happy with the latter at half the price. The only problem?.. does not talk to OS Sierra but it does to old versions... so I guess its just a 'wait and see until there are a bunch of updates to the operating system' and perhaps then these things might just work.
The moral is not to update the OS until it has been out at least, say, a year.