I've had a couple of PMs about this - sorry didn't see them until this morning - so thought I'd copy my reply in here for all to see. As mentioned before, I have to thank Ronie from Transparency for his help with this, I wouldn't have had a clue otherwise!
You need to alter the home.xml, includes.xml and musicvisualisation.xml files – these are located in appdata/roaming/xbmc/addons/skin.aeonmq3 – If you’re doing this to a different skin then the file names may be different but the location should be the same, I believe.
For each file you need to change the texture fallback code for the CDart to include a diffuse image. For safety, best to backup the three files before playing with them.
You also need to add this
disk_mask.png file into the media folder of the skin. I’ve also put in there this
disc.png file – not sure if you need that one or not but it can’t hurt.
If you open each document in notepad and then use the Find command to find “CD Overlay” - a few lines later you will see the texture code.
If you change this;
<texture fallback="cdart.png">$INFO[Player.FolderPath]cdart.png</texture>
To this;
<texture fallback="disc.png" diffuse="disc_mask.png" background="true">$INFO[Player.FolderPath,,cdart.png]</texture>
On the includes.xml file I also had to alter the size and position of the cd image, as it was slightly larger than the folder image – this is the code just before the texture code and I changed the size from 56x56 to 50x50 and the position from 22 x 3 y to 33 x 7 y – not sure if you’ll need to do this, see how it looks first maybe and then play around with the numbers.
I’ve also changed the size of my folder image on the home.xml and musicvisualisation files, as I use a slightly different cd case image – my folder images are slightly smaller because for the past few years I've used a program called stark covers to add a sheen to the image and round the corners and as a result of this the image is slightly smaller so looks better in a different cd case.
This was a program I found whilst using WMC Media Browser (pre-XBMC days!) – as I’d altered my entire music collection folder images, it’s hard to go back now!!
Hope this helps a few people.