Joren,
I think if you take out the CSS classes form the navigation menu items there, the images should be visible. That’s what I would try first.
If that doesn’t do the trick you can add this to your Custom CSS:
#social li.dribbble a,
#social li.email a,
#social li.facebook a,
#social li.flickr a,
#social li.foursquare a,
#social li.forrst a,
#social li.google a,
#social li.github a,
#social li.instagram a,
#social li.itunes a,
#social li.linkedin a,
#social li.pinterest a,
#social li.twitter a,
#social li.youtube a,
#social li.vimeo a,
#social li.yelp a,
#social li.podcast a,
#social li.rss a {
text-indent: 0;
background-image: none;
}
Bill