Aeon by itself uses SD fanart since it occupies just half the screen (CD Cover on the left, Fanart on the right).
When you went to Aeon Lowlist, all your fanart has to be recreated.
in the skin directory, look for the file skin.properties.
Look for the section "fanart.movie.width" and "fanart.movie.height"
For Aeon lowlist, you have to set the width to 720p (no higher) which is;
width=1280
height=720
Then you have to recreate the jukebox from scratch