I am searching for the same thing and see that nobody has answered your questions.
Specifically, I have a 16Gb USB with MP3's encoded at 192kpbs with IDTags ver2.3 that include album art. My X920 does not display the art although it shows up on my computer when viewing the files in explorer using Win7/64.
Does the X920 not display the art even though the documentation states that it is compabible with IDTags ver2.3?