Don't output the avatar, as it's directly use
wp_list_authors but it's a good starting point. I've finally choose to rewrite a
wp_list_authors_with_avatar that make the job I want.
Honestly, the need to rewrite a 60 lines function just for add an avatar in a listing (or just because you want the rss icon before the name) look like if the templating system is flawed somewhere. Why not an author loop? Something like:
<?php if (have_authors()) : while (have_authors()) : the_author(); ?>
<?php the_author_rss(); the_author_name(); the_author_avatar(); ?>
<?php endwhile; else: ?>