"To madden" means "to make crazy",(as in "maddening") so IMHO this is not a good name at all. But if this doesn't bother you, the best mns are
Oliver and
Julius.
Maddie/Maddy does sound a bit girly, because I associate it with
Madeleine. But since it's ok for girls to go by
Chris or
Charlie, there's no reason why shouldn't be ok. for boys to have girly nns. And Madden is weird enough to my ears that a nn won't make it weirder.