The main screen of Playing Now shows a large cover in the centre of the screen. As mentioned, the default behaviour can be changed, and <left>/<right> will change it to a visualization or remove it. The "Info" screen of Playing Now is the "large" file info panel used in Library views. It includes a cover on the right. The size of the cover can be set in Options > Theatre View > Customize file info panel... (select the Audio template) > Manage > Edit > Style.