Thanks for the clarification. It is mentioned in the second edit to the post.
As far as I know it is not possible to have a direct download. You must use either the Galaxy client or the GOG Downloader.
It'is not true. You can download all the package (game+dlc+bonuses) directly from the site without problems. I tried some minutes ago. I do not use GOG Galaxy and I have just installed the game from the site.
Edit: Only to be clear, I downloaded the preorder bonus some days ago with the same method. bye
Downloaded everything directly from the site. Just click --> save as... You know...
If you click with left mouse on the item (with decent browser like firefox or chrome) you obtain the same effect :)
Yes I know that is now the case. Please take a look at the changes and updates that were made quite a while ago to the post and the correction given by other users as well (Edit 2).
Adding more credible sources who have tried these methods is always nice so thank you both.
Restarting your client.
I personally didn't have this problem nor did anyone mention it yet but the Galaxy client has a lot of UI updating issues so I would suggest that is the case.
I have, multiple times. I hoped the issue would resolve itself after I woke up but it's still here.
Please try to download the DLCs manually from the site using the method in Edit 2 (from your account page