You're not really going to add muscle to your butt without adding muscle everywhere else. Also remember that your glutes are huge (the actual muscle, not specific butts) so putting size on them can be a process. When you are trying to add size you need to use some good weight, and do sets where you fail at no more than 12 reps. Only take your last set to real failure, but be sure to make the rest of the sets count. If you are already doing squats and lunges with a barbell then you're definitely on the right track. Make sure you do your squats as deep as possible. The deeper you go the more it involves your glutes. I think the last machine you are talking about is a butt blaster. I've never used one, but it definitely seems like something that would work. Deadlifts can also destroy your glutes depending on your body structure. I've never seen a lighter weight female powerlifter or weightlifter without a nice ass. This is mainly due to squats and deads.
The only other exercises I would suggest are pull-throughs and glute ham raises. I do both of these and my ass is always sore, har har.