Using the user's theme-icons is very hit and miss because not all themes have the same type of icons. Additionally, the freedesktop icon-naming standard are rather limiting for multimedia i.e. no volume icon.
Using the Amarok-1.4 icons, where they are available, just does not seem to look "right" as made evident by the image below.
What I will go forward with still is not ideal but shall be this:
- User's theme-icons with the Tango iconset filling in where possible (Default).
- Amarok-1.4 icons as an option, perhaps.