Two things, first, slimboxplus wasn’t created by the author of Slimbox (not that that would be a problem).
Second, and much more crucial, slimboxplus uses the old MooTools reliant version of Slimbox, and not the jQuery reliant Slimbox2, as such you will not be able to use this version with the plugin.
Talk to the slimboxplus author and see if you can talk him into making a similar version for slimbox2, and if he does let me know and maybe we can do something .