Hello, you won't like this, as it might damage the text on your speakers, or not....
For cleaning this type of thing, I use 'Novus plastic polish 2' available in the US ( Web
http://novuspolish.com )In my experience, using this polish with
light pressure will remove stains without removeing printing, but of course, try on something else first. I have had luck with this cleaning up A1200's, and a couple of C-128's, but there was no printing...
Hope this helps..