I've written several bash scripts now to display Amarok's track data and cover in conky. Since my script folder started to get a bit crowded, I decided to clean up and pull everything together into just a couple of scripts.
I still use Amarok 1.4 in Gnome. Here everything works as intended. Included is also an Amarok 2 script, but I haven't tested it much on KDE. So if you find anything that needs correcting then please let me know so I can make the changes.
Due to the way Amarok 1.4 and 2 provide their track data there are quite a few differences in what is available for each. Check the README file for all the options.
The above screenshot does not show all the cover styles. There is a 5th plain style (default) which simply returns the coverart and resizes it to 150x150.
Another option is to display the coverart in greyscale.
Both the style and colour/greyscale can be specified from inside the conky script which makes changing the look easy.
The README file contains all the instructions you should need, including installation. There's also a sample conky script.
It also shouldn't be difficult to adapt the cover script for other players.
Note: I couldn't get the stack style to work with Amarok 2 in KDE.