He does look a bit ribby - in the first pic you can see the bottom of his ribs. But honestly, he looks really good otherwise. He doesn't need too much more, if you can get another 10-15 pounds he'd be perfect.
The lighting isn't perfect but from the top down pic he looks fine too, it doesn't look like his spine sticks out. Feeling it is usually fine (especially for the long lean Dane body) but showing it is not. Sort of like horses, feeling ribs well is fine, seeing them is not.
I'd focus on just finding a food he likes and stick to that. If he likes the lamb and rice, give him extra lamb and rice. First and foremost is to get him to a weight you like, but don't fret about it - he's not unhealthily or dangerously skinny.
Also, he's GORGEOUS. :)
ETA: ClaPorte is right. Neutering should give him a good 10 pounds.