Calibre then imports the files, which will include updated versions of previously imported files, which you can choose to redownload if you desire. You'll notice a lot of files with the same gibberish name but different formats, but only one version of the file is not greyed out - the.
Once you have done that, you just open up Calibre, select 'add books' and go to wherever you put the aliased 'My Kindle Content' folder. You may need to select individual titles and download them as well to make sure the number of titles on device matches the number in the cloud. Now go to the Mac, and open up Kindle for Mac and do a sync.
#Kindle for mac document files in cloud portable
You can make it your default device, but if you read on a phone or other portable device, that's not very useful. Then select the content you want to download (10 items can be downloaded at once), and select 'Deliver' and make sure 'Kindle for Mac' is ticked in the list. If you use collections in your Kindle app, it is useful to add the content to a collection as you can see which hasn't been added to one easily. Again, it is useful to sort by date, most recent first. Go to 'Manage my content and devices' at Amazon, and locate your newly-purchased content.
Make sure the aliased version is sorted by date, most recent first. The best way to do that is to go to Finder and search for it, and make an alias of the folder, either by highlighting the folder and doing 'Cmd-M' or selecting 'Make Alias' from the pop-up menu, and then dragging the alias to the desktop (or to your favourite locations list in the left side bar in a directory window). The main issue is finding the 'My Kindle Content' folder which is buried somewhere.
I'm away and won't be home until tomorrow so I'm doing this from memory.