Is the dog “skinny” or “lean”? There is nothing wrong with lean.
Intact or neutered? Intact males tend to be more lean than neutered ones.
If the dog is infact eating 6 cubs of the kibble you mentioned, this dog should not be “skinny” , if it is, there is something medically wrong.
Boxers are generally lean dogs, with deep chests and narrow abdomens. You should be able to see a hint of ribs due to their chest conformation.
It sounds like this dog needs to see a vet, get an accurate body score index based on the breed done. Just because routine bloodwork is normal doesnt mean the dog is healthy.
