Gracenote Database - how to add Cover Art manually if not found automaticaly

@hgeifman,
first of all thank you very much for your ongoing support and your attempts to help me in this matter.
I followed the links you sent me in your previous post - very interesting information but does not exactly meet my case.

I am rather familiar with finding album covers in the internet, making screenshots or simply taking pictures from the covers, crop them, save them as jpegs, named as Folder.jpg, and place them into the appropriate music folder at the bottom end of all music titles - this worked fine with dBpoweramp on my MacBook Pro.

BUT: unfortunately NO music folders of all CDs ripped by the A&K 500n show a folder.jpg or cover.jpg, although the cover images are displayed during search or playback!
And so far I found no location or folder on my A&K 500n where images could have been stored - there is a "ripped folder" that shows all ripped CDs as separate folders with the album name, but there are no jpegs inside (I accessed the HD of the A&K 500n by an USB-connection with my MacBook)

The A&K 500n is an almost perfect ripping server that would do everything automatically, but I can't be sure whether it finds cover art or not! (currently I am not ripping those CDs when Gracenote can't find the cover art - waiting for a solution to rip them later!)

As the hardware and the ripping software are SOTA (the A&K 500n sounds absolutely fantastic) I would not like to import complete folders from previous rips with my MacBook and dBpoweramp (the databases used by dBpoweramp (MusicBrainz, AMG, GD3, freeDb etc.) rather often did not find the CDs or title information either, so buying the A&K 500n was also a decision driven by the Gracenote DB.

What I tried successfully was importing a complete folder previously ripped by dBpoweramp incl. the Folder.jpg - the music was played flawlessly by the A&K 500n and the correct cover image was displayed - crazy!
What did NOT work was moving an A&K 500n ripped CD folder without album art to the desktop of my Mac, adding the cover image and moving back the folder to the A&K 500n - absolutely crazy!

Sorry for the length of my reply to your suggestions - but thank you anyway for your efforts in this matter!

@collectoratad, Obviously, none of my suggestions above solved your album cover art issue.   Please call Astell&Kern Customer Support for help.   Please see link, phone # and email address below.

https://us.astellnkern.com/pages/contact-us

Email: support@theinvixion.comPhone: (949) 336-4540/4541

@hgeifman 
Again thank you very much for your efforts to help me in this matter.

I tried your method with iTunes to find cover art - that worked fine, I was even able to load jpegs that I have previously shot with my iPhone and saved as jpegs.

Furthermore I have tried different file formats (jpg, jpeg2000, png, exr) and different name options (cover, Cover, Folder, folder) - nothing worked!
I switched from FLAC to WAV but no difference with the album art!

Probably one reason is, that the only way to access the AK 500n is through a 3rd party SW named „Android File Transfer“ which doesn‘t allow any Mac commands- its only for file transfer to or from the AK500n.
I have already emailed Gracenote support but have received no answer (it seems that they are not responding to end users at all!)

I will try to email the Astell&Kern support but based on my experience they will not respond to customers outside the US (I‘m based in Austria/Europe)

I was hoping that some other AK 500n users (which should have the same issues) would share a potential solution with me .... unfortunately no one so far!

I will keep you posted if I find a solution - but only if you are interested (I do not want to further bother you with my problems)

Thanks again for all your suggestions and support and best regards,
Carlo